A/C Woes

[Mike534x]

Alrighty! So I don't throw off the "What did you" thread, I made this one to post the issues I'm having and what's been done. This thread will cover both trucks, but the main focus will be on the Envoy.

So a run down of what's been done;

Envoy
- New Denso A/C Compressor, and AC Delco Dryer/Accumulator as of 6/13/24
- A/C Recharged twice in Summer of 2023 (Shop that services our work vehicles did the service, still didn't blow super cold. Second shop that does our alignments/most of the work looked it over and said it was overfilled. Blew cool, but not cold cold. Temp gauge attached to the center vent showed 70*, and 55-60*F being the coldest with Auto-HVAC set to 60* with re-circulation/max fan.
- EV Fan Clutch swapped to a Thermal Clutch (Used unit pulled from a 2008 TrailBlazer) as of Summer of 2022
- A/C Condenser replaced in Summer of 2017. Shop found a hole where it blew, and send debris into the system. Worked "somewhat" okay but gradually got warmer as the years went by.

A/C worked fantastic in the Envoy after the new compressor and accumulator were installed, took 5 minutes to blow ice-cold but no biggie. The shop is roughly 40 minutes away from home, and the temp reading I was getting from the gauge stayed at around 42-48*F, which is a significant improvement over the last few years. I did notice that the air got less cold at idle/at a stop, where it would go to 50-55* but would drop back down again while moving. Fast forward to today, left the house at 9 AM to run errands/shop and the ambient temp outside was 92* F. Got in, A/C started blowing immediately cool, got about 10 minutes from home and she was sitting at the same readings (42-48* while coasting) beforehand. Pulled into the shopping center, got out, and got back in about an hour later. Noticed its not blowing as "cold" as it did leaving home. Continued driving around, and the gauge was reading 60*F from the vents, even with the recirculate button on (could hear the change in the actuators when pressing it). Drove around some more, and the gauge fluctuated between 55-60*. Noticed that during the fluctuations, I could feel the air getting "slightly" warmer, with that brief "smell" (I can't describe it well) that comes when the compressor cycles off/and it stops sending cold air through.

So now its underperforming, and almost acting like it did the prior summers before it failed. Some suggestions were testing the fan clutch, so if its doing this in stop and go/semi-city driving....would it be better on the highway? Not exactly. I figured if the clutch is acting up, then taking it on the highway with more airflow hitting the condensor should compensate for it (at least thats what I assumed). Drove for about 35 minutes with no traffic, and it took 30 minutes before the air from the vents finally was reading 48*.The moment I got off and came to a stop it shot up to 60*.

Which has me questioning, is the system overfilled, or undercharged?
Did the shop replace EVERY seal as instructed (including the high side at the condensor, not just the compressor/accumulator)
Did they replace the orifice tube and valves (I provided those in the package with the new A/C belt and tensior)
Is my 7 year old A/C Condensor junk/clogged from whatever made its way into the old system?
Thermal Clutch is spinning enough to prevent an overheat, but not engaging to fully move air through the condensor?

At operating temp, it does feel like the thermal clutch is working. When attempting to stop it, it did take some effort to slow it down, but not stop it. I did notice it took a bit a brief moment for it to "catch" and spin back up to speed. It certainly looked and felt nothing like the old EV clutch that just gave up on spinning fully after stopping it. One thing I found odd is, it doesn't roar on cold starts after sitting, or even hearing it on hot days. Operating temp sits between 204-209, so its not overheating.

 

[TJBaker57]

By any chance are you a Torque Pro or similar user? If so I might be able to help set up to monitor AC high pressure and perhaps even some other useful data like the low pressure switch status, etc.

Are both vehicle CJ2 digital automatic systems?

 

[Mike534x]

I have Torque Pro! I followed a past post with the PIDs (from yuor excel sheet) for the Knock Sensors when I was having an issue with a faulty CEL on the Trailblazer.

I don't know if they are both CJ2 Digital systems or not.

 

[TJBaker57]

Ok then, one thing I would do is get a look at you AC high pressure during some driving.

The usual Mode&PID is 221144. I almost always append 01 to that for 22114401. The units are PSI and the equation is something like A*1.833-15. There are slight variations of the equation but this is close enough, no need to split hairs here.

Now as for the header my vehicles are both older and do not use CANBUS protocol so my header is 6C10F1. I think both of your vehicles will be CANBUS so I am uncertain what the header should be though it will NOT be what I use. Perhaps try with the header left blank.

I just recently picked up an 08 ECM for a 4.2 so I can have a look at that tomorrow to see what works.

I don't know if they are both CJ2 Digital systems or not.

CJ2 is the RPO code for the automatic control system. That will have rotating knobs for temperature settings. The CJ3 systems have vertical sliders for temperature settings.

 

[Mike534x]

Ok then, one thing I would do is get a look at you AC high pressure during some driving.

The usual Mode&PID is 221144. I almost always append 01 to that for 22114401. The units are PSI and the equation is something like A*1.833-15. There are slight variations of the equation but this is close enough, no need to split hairs here.

Now as for the header my vehicles are both older and do not use CANBUS protocol so my header is 6C10F1. I think both of your vehicles will be CANBUS so I am uncertain what the header should be though it will NOT be what I use. Perhaps try with the header left blank.

I just recently picked up an 08 ECM for a 4.2 so I can have a look at that tomorrow to see what works.



CJ2 is the RPO code for the automatic control system. That will have rotating knobs for temperature settings. The CJ3 systems have vertical sliders for temperature settings.

Ahhh my mistake! I didn't know that was the RPO code for the Digital HVAC, both trucks are equipped with them.

 

[Mooseman]

After @TJBaker57 helps you out with getting the high pressures and compressor commanded state, it might be worth it to get a set of A/C gauges to find out what are the true pressures, both at rest and while operating, which may tell us if it is overcharged. They're not that expensive at HF and Amazon. My TB was under performing and cycling the compressor excessively. The gauges told me right away it was low.

I doubt the clutch is failing. Have seen them not work well once hot but would be very surprising with your new Denso compressor however have seen the quality of name brands take a dump lately. When you find out the commanded state of the compressor and see what it's doing, that should confirm it.

Do you know if the shop that did the work replaced the shrader valves, especially the high side? The original high side one is just a rubber ball and is prone to leaking. Good shops will always replace these with a real shrader valve. (Which reminds me I have to replace mine next time it's low).

If it's determined that you're always losing refrigerant, it would be a good idea to get an A/C leak detector, also available fairly cheap at HF and Amazon. I got one years ago to detect a leak on my 02 that confirmed that my evaporator was leaking.

Is the Envoy an XL or XUV with a dual system? If not, sometimes shops will overfill the system as if it was a dual system thinking that the center console vent is a secondary system when it's not.

 

[Mike534x]

Envoy is just the regular SWB, with that center console system. The clutch stays engaged on the new compressor, but its when driving that it feels like its disengaging briefly before going again. I am curious to know if they tried filling the system with the XL/EXT specs ( think the SWB is 1.9 lbs?). It looks like the high-side valve was replaced with the same style one. I've got an appointment when they open at 9 AM to have it looked at again, I'll see if they can provide me with the low and high side pressures. I went out last night with my UV black light, and I don't believe they replaced the seals on the low and high side on the condenser. Judging from the neon green, it looks like my leaks been originating there since the dye was put in last summer, and the area/bolts there don't look like they've touched very recently either (too much build up around the bolts, and where the tubes line up).

The Trailblazer is the one that's currently having issues with the clutch disengaging after 20 or so odd minutes, and it will start working again after its been left off for a few minutes. Which leads me to think the clutch is worn, or its de-energizing itself from the shim being out of spec. I'm not entirely sure, its going back in after the Envoy is dealt with.

 

[Mike534x]

I'm at the shop now.

Low side is reading 35 PSI
High side is about 250 at idle.

They're removing some of the freon now, and doing more tests. Looks like it may be overfilled.

 

[TJBaker57]

The shop didn't weigh in the correct charge per the sticker on the vehicle ? ! ? !!!

 

[Mooseman]

They should evacuate the entire system, replace that rubber ball type high side port, and refill the correct amount. I'd also replace the orifice tube while the system is empty. Cheap insurance.

 

[Mike534x]

Yeah...I may be taking her the shop that does our work normally, and have them do a proper "charge". They fill it until "the high side hits 200", then he commented that the low side was too high, and I told him no. The low side should be between 31-44 PSI. They just removed enough to where the high side stayed under 200, and they didn't evacuate it either to re-check the seals or orifice tube. So yeah, I'm not sure I'll be going back to them. So my confidence in them getting it correct again are....very low. Its blowing at a consistent 45* now, even at idle, but I feel it could be a tad bit colder.

Though, I may just run to Harbor Freight and get everything I need and take the system down myself, and refill it. They "claimed" they installed the new orifice tube/seals, and valves but I still don't fully believe it.

 

[Mooseman]

You would need an actual A/C machine to recover the refrigerant from the system. Not something easily done at home. If it's been emptied, you can evacuate the air from the system with a vacuum pump and refill with the appropriate amount.

Wait and see how it works now. If it's been brought down enough, it might be OK.

As for pressures, it's not a straight answer. It's also dependent on ambient temperatures. The hotter it is, the higher the pressures.

 

[Mike534x]

Welp that was short lived. It's not running correct, been driving around for 20 minutes (10 mins with remote start before doing so) and it's back to blowing 60 straight from the vents. Sitting at idle it's 65*

Ambient temp this morning was 82* and it's about 89* with the humidity.

 

[Mooseman]

You need to see what the compressor is doing and get your pressures when it happens.

 

[Mike534x]

So the new things it's doing;

Blowing semi cool at 70* from the vents, and blowing warmer as you start driving. So they either took too much out, or they screwed something up with the new compressor.

The shop I normally use wants it dropped off tonight, and he'll do a full inspection and test everything out tomorrow morning and let me know what they find.

 

[Mike534x]

Trucks been dropped off to our regular mechanic, I should be by tomorrow afternoon what they find.

I called shop #1 back, and they're excuse is "Oh it's probably a bad compressor, especially if it's turning on and off". Yeah...maybe winging the freon you guys dumped on, and took out had nothing to do with it.

Onto the Trailblazer;

Pulled the A/C relay as soon as the system stopped blowing cold air, and damn that thing was super hot to the touch. The new one isn't here, so I swapped over the one that controls the Air Solenoid as a test and it started to work again. I've got a 30 min drive for work tomorrow, so that'll be enough to see if the relay may have been tripping out for the compressor.

 

[TJBaker57]

The low side should be between 31-44 PSI.

pressures will be affected by the rpm of the compressor, the airflow over the condenser, the airflow over the evaporator, the wet bulb temperature of the air over the evaporator, the ambient temperature of the air over the condenser and so on.

charts are just ballpark figures assuming some standard conditions that may or may not apply in each particular case.

I hit a deer a few years back and had to replace the condenser. I sealed the lines the next morning after the deer incident and I live in a dry climate. I replaced ONLY the condenser. Triple evacuated and added the specified charge plus some oil and the damned thing blows 32° with the original 2001 compressor!!

 

[ultra...good]

pressures will be affected by the rpm of the compressor, the airflow over the condenser, the airflow over the evaporator, the wet bulb temperature of the air over the evaporator, the ambient temperature of the air over the condenser and so on.

charts are just ballpark figures assuming some standard conditions that may or may not apply in each particular case.

I hit a deer a few years back and had to replace the condenser. I sealed the lines the next morning after the deer incident and I live in a dry climate. I replaced ONLY the condenser. Triple evacuated and added the specified charge plus some oil and the damned thing blows 32° with the original 2001 compressor!!

View attachment 113398

Isn't that too cold though? Risk of ice forming, too much of a good thing, if there is a problem too have etc.....

 

[TJBaker57]

Isn't that too cold though? Risk of ice forming, too much of a good thing, if there is a problem too have etc.....

I get away with it because the climate here at 8000 feet in southern Colorado is damn dry. We're talking like 15% humidity. In a more humid climate my discharge temperature wouldn't get so low due the latent heat load.

 

[Mike534x]

I didn't think these systems could get so dang low! I'm impressed and jealous.

New Relay is going in tomorrow! Seems to match up part number wise to the original.

 

[ultra...good]

I didn't think these systems could get so dang low! I'm impressed and jealous..........

+1

 

[ultra...good]

I get away with it because the climate here at 8000 feet in southern Colorado is damn dry. We're talking like 15% humidity. In a more humid climate my discharge temperature wouldn't get so low due the latent heat load.

Brings up another question or lacking a better term? I had to wrap my head around the part about latent heat and the discharge temperature in relation to a freezing coil.

That discharge temperature would assumably be cold enough to freeze any moisture at the coil. Under 40 discharge in WI with 60% and ice quickly.

Now I realize my question: is your coil forming ice just not enough yet to notice an issue?

 

[Mike534x]

Shop got back to me about the Envoy, and it's ready.

They did a full evacuation, and pressure tested everything. All the valves and seals are checked out, and it's been recharged. System was still overfilled by a half pound. I'll have to pick it up tomorrow before work, but they're getting about 53* out of the vents at idle, and about 40* while driving.

So far, it sounds like my regular place has it dialed back in. I'll know for sure when I'm driving and will report back with how it's doing.

Now onto the Trailblazer. New relay is in, and it's still acting up. I felt it going out at the stop light, switched to neutral and revved the engine a bit which brought it back to cold for about 2 minutes before it went out completely. I took the thin handle for my tripod, and tried tapping the face of the clutch/pressing against it to see if that would cause it to re-engage and it didn't. So it doesn't seem like the clutch is the issue. I'm beginning to wonder if the high/low/ or temp switch on the compressor itself is acting up and tripping it.

Normally when it stops working, if I shut the truck off and wait a minute to restart it'll work for the next 20 minutes but this time it stayed blowing warm.

 

[budwich]

I don't believe the system is a "constant on" system... meaning it disengages the clutch when needed due to pressures. As was posted in back (#4), get some way to monitor your compressor pressures (live data reader), that will tell you what's up when you feel things are shutting down or not cooling well.

My limited experience with a similar event / issue is that you have a clutch / compressor issue. The coil on the clutch is not able to keep it engaged due to an electrical issue (low / high winding impedance) or the gap (wear) is too great for the electromechanical force to maintain / achieve. I had similar results, where by, the system was working fine but in traffic / high temps, cooling would stop. Shut off the engine and restart, in most cases, it would go back to cooling again for a short while until temps would build. Remember that high pressures increase as the temps go up putting more strain on the compressor and the clutch holding force.

 

[TJBaker57]

Brings up another question or lacking a better term? I had to wrap my head around the part about latent heat and the discharge temperature in relation to a freezing coil.

That discharge temperature would assumably be cold enough to freeze any moisture at the coil

So play around with the calculator here at the link below and you will find the dewpoint for air at 75 degrees Fahrenheit and %15 relative humidity is about 24 degrees Fahrenheit. Simply put, there is not enough moisture in the air here for icing to be an issue for me. And on days when there IS enough moisture in the air the extra load of removing moisture at the evaporator raises my discharge temperature.

Dew Point Calculator

This free dew point calculator calculates dew point, relative humidity, or air temperature if given any of the other two values.

www.calculator.net

 

[Mooseman]

Like @budwich said, it could still be a failing clutch coil. When it won't work, you could try a couple of things. You can pull the connector from the low pressure switch and jump the terminals. If it's the switch or it's low, the compressor will come on with the jumper. If it still doesn't come on, try to jump the A/C relay. If it still doesn't come on, I would suspect the coil is dead but still confirm the wiring is good getting power to it. I replaced my coil and it's still working great.

A/C Clutch Kit from AliExpress (how to replace)

 

[Mike534x]

Like @budwich said, it could still be a failing clutch coil. When it won't work, you could try a couple of things. You can pull the connector from the low pressure switch and jump the terminals. If it's the switch or it's low, the compressor will come on with the jumper. If it still doesn't come on, try to jump the A/C relay. If it still doesn't come on, I would suspect the coil is dead but still confirm the wiring is good getting power to it. I replaced my coil and it's still working great.

A/C Clutch Kit from AliExpress (how to replace)

I can try giving it a shot when it acts up again! I had a spare low pressure switch (new) that I installed when it initially started, otherwise it was working fine mid-May the one weekend it was hot and drove it that whole weekend without any issues. Then whatever reason, it started acting up a few days later.

Which has me wondering if the coil was already on its way out, but it was accelerated due to the rapid heating cycles we've been having up here the past month. Its just so odd it went from working one weekend, to not after just a few short days. So it might be safe to assume, that if the coil is dead, then everything before it was just it working on/off after it started heating up until it just stopped? It starts to work after its been sitting for a few hours.

It actually slipped my mind the last few days, I've been so focused on trying to decide which truck to tackle. I had intended on ordering the clutch kit, but came across a compressor pulled from an 09 Trailblazer that was wrecked (had 40k on it). Price was about the same with shipping as the clutch. I figured it didn't harm to get it, and with the age/miles it should still be healthy. Then buy the kit, and refurbish the old compressor myself with the new clutch, and maybe replace the sensors and I'll have a working spare for down the road.

 

[Mike534x]

Well got the Envoy back. I'm still not happy with the way this thing is acting. Idle temp is 65* out of the vents, and if I'm staying still with the idle raised it starts to blow cold down to 50*.

So should I consider that I've got an airflow issue regarding the clutch, or maybe this condenser has a restriction?

Second edit:

It's about 75* right now, and the humidity is low so it's not hot hot like it was earlier. Went out on lunch break, and left the A/C running and it's still getting 60 out of the vents. Raising the RPMs causes it to quickly cool, and it's dropping to 50* and then starts to shoot up to 60, back to 50, then to 60 and it's just going back and forth without settling.

 

[Mooseman]

Could be the fan clutch. Even thermals can fail. How much air is it pulling? Apparently the aftermarket ones don't work as well as OEM.

 

[Mike534x]

Could be the fan clutch. Even thermals can fail. How much air is it pulling? Apparently the aftermarket ones don't work as well as OEM.

It seems to be pushing decent air, or at the very least seems to be spinning. I did order another off Amazon to test it, when doing the clutch test it did take a bit to spin back up to speed. Idle temps are stable at 208* according to Torque. I'm fairly certain the thermal from PnP was a OEM unit.

Though I am questioning myself if the condenser is the issue, or if the old one (comp) sent debris or junk through and it's just plugged up resulting in poor pressure build up at idle. Which wouldn't explain why it was blowing cold cold and now poorly with the proper amount in it. But I also can't help but wonder if the compressor was damaged by the first overcharging also.

 

[TJBaker57]

Idle temps are stable at 208* according to Torque.

And have you got the AC High pressure reading in Torque as well?

 

[Mike534x]

And have you got the AC High pressure reading in Torque as well?

I'm working on setting it up today! I was waiting, because I bought a set of high and low pressure gauges to arrive. But I noticed that Torque had a preloaded value/PID for the High Pressure side. When connected to the Envoy, it was giving me a baseline reading when testing it. Included a screenshot of the values, but I also added the one you posted.

Is there a PID for the low side also, to monitor both while driving?

@budwich Are you referring to the AC compressor issue for the Trailblazer? Or do you think the compressor might be bad for the Envoy?

 

[budwich]

tjbaker57 provided a "working formula" back in post #4. The pid's may not align. You need to see if your value / formula provides anything. IF not, you can add / try the one posted. I used his "corrected formula" on my 2008 as the existing one didn't provide a very good number. I have to check what the pid finally is.

NOTE: the pid pressure reading is a "real pressure reading" meaning, the system pressure is being read / monitored. It ranges from "normal low" (compressor off) to "high compressed" (compressor on) levels. Basically, from my limited experience, when you monitor it, you basically don't need any gages as it is providing an "overall pressure reading" of the system... it kind of works out that way in the system design. The low pressure switch is another point of "mechanical control" for the system. Ultimately if you have a set of gages, you can compare their readings with the PID as it "cycles". The readings might not match exactly but will close enough to likely determine how things are.

As for my comment about the compressor / clutch, I was referring to your trailblazer which you were indicating a shutdown and restart causes the system to work again... along with a hot relay.


ADDED: I just checked my torque on 2008. The pressure equation is as posted by TJbaker57 while my pid is 221564. Not sure where that came from but might have been "discovered" along the way.

 

[TJBaker57]

But I noticed that Torque had a preloaded value/PID for the High Pressure side

That 221564 PID is not going to work, at least not with a 4. 2 engine. That PID ## is not supported. For a 4.2 you need a 221144 PID ##.

When connected to the Envoy, it was giving me a baseline reading when testing it.

Not sure what you mean with this statement.

Is there a PID for the low side also, to monitor both while driving?

No, there is no pressure sensor on the low side, only an on-off switch used for 'cycling' the compressor. For some TrailBlazers I have a PID that can display the status of that switch, on or off.

Even if you don't have a Torque display for the low side you will know when the switch opens or closes by the resulting rapid rise & fall of the high side pressure.



The thing about reading high pressure with Torque Pro or similar,,,, anyone with an OBD adapter and the right PID can monitor the high pressure in real-time driving. It will show immediately if the compressor is running, how fast it cycles, what is the high pressure cycling at (high and low) and more. Without spending a nickel. Manifold gauge sets are a good tool but you can't tell what is happening as you drive around town. Well, I can do that because I have been and HVAC tech since 1984 and I have the equipment to do that

You can learn a lot about how your AC system is working by observing it in real life driving as opposed to what you witness parked in a driveway.

 

[Mike534x]

That 221564 PID is not going to work, at least not with a 4. 2 engine. That PID ## is not supported. For a 4.2 you need a 221144 PID ##.



Not sure what you mean with this statement.



No, there is no pressure sensor on the low side, only an on-off switch used for 'cycling' the compressor. For some TrailBlazers I have a PID that can display the status of that switch, on or off.

Even if you don't have a Torque display for the low side you will know when the switch opens or closes by the resulting rapid rise & fall of the high side pressure.



The thing about reading high pressure with Torque Pro or similar,,,, anyone with an OBD adapter and the right PID can monitor the high pressure in real-time driving. It will show immediately if the compressor is running, how fast it cycles, what is the high pressure cycling at (high and low) and more. Without spending a nickel. Manifold gauge sets are a good tool but you can't tell what is happening as you drive around town. Well, I can do that because I have been and HVAC tech since 1984 and I have the equipment to do that

You can learn a lot about how your AC system is working by observing it in real life driving as opposed to what you witness parked in a driveway.

Got it! I'll input the equation for the Trailblazer, wasn't sure if both were different between the 5.3 and 4.2. I just got off of midnight's, so my thought process was a bit out of it when trying my "baseline" reading comment. I had meant to say, that the 5.3 PID does seem to be giving me a reading so I'm definitely curious to see the pressures I'm getting while actually moving. I figured getting actual gauges wouldn't hurt, and hopefully teach myself a bit more then what I know currently!

I know the system is capable of producing cooler air, my regular guy that did the correct charge is telling me this is the best it'll get and that I shouldn't expect much from having a "hot running" V8 under the hood. After having a prior 5.3 Trailblazer that would freeze me out, I know something is definitely off with the Envoys system.

@budwich Thanks for the clarification! Sorry, between two vehicles suffering different problems it's been a bit hard keeping track of it all. With you having a similar issue, I fully do believe the problem lies in the compressor/clutch. I've got the "new" used low mileage unit, seems to be in good shape, and turns smoothly by hand. Just waiting on the new seals and dryer, and a not so hot day to get it yanked out whenever I get it back.

 

[Mooseman]

It's possible your previous TB had a low charge, which can cause freezing or a faulty low switch that would either get too low pressure or didn't cycle like it should. Had that once and the evaporator would freeze solid and no allow air through.

 

[Mike534x]

It's possible your previous TB had a low charge, which can cause freezing or a faulty low switch that would either get too low pressure or didn't cycle like it should. Had that once and the evaporator would freeze solid and no allow air through.

Thats a possibility too. I never had issues with it freezing up, but temp wise I do recall it feeling identical to the current TB when the A/C does work. Cold enough to be comfortable when it's hot, but cooling down the interior enough to lower the fan speed. Compared to now where it's just barely enough to keep you cool while driving.


The only issue I've had with frost, was on the Envoy. Shortly after the condenser was replaced, the accumulator had a thin layer of frost build up, and on the lines going to the firewall/evaporator. Found the low pressure switch was bad when trying to jump it, and it never happened again. Just every summer the decline was noticeable with it blowing less cool each year. It ran perfect up until the condenser went out, and just became a domino effect.

 

[budwich]

That 221564 PID is not going to work, at least not with a 4. 2 engine. That PID ## is not supported. For a 4.2 you need a 221144 PID ##.

I know this is potentially "funny".... but it works on my 2008 4.2.... but I don't know where it came from in my travels.

Anyway, go with what works... you can always verify with your "hard gages".

 

[TJBaker57]

I know this is potentially "funny".... but it works on my 2008 4.2.... but I don't know where it came from in my travels.

Well this is good information! I had ASSumed that since it didn't work on my 2002, 2003, 2005 and 2006 4.2 PCMs that it wouldn't work in the others. It also does not work on my 2005 5.3 Yukon.

Both my Yukon andy Trailblazer discharge at mid to low 30s °F.

I'll post up a graph later showing what things look like while driving. Car Scanner ELM OBD excels at displaying and recording real-time PID data.

 

[budwich]

I think this was bought up a while back when I was having AC issues (as stated herein) and I pointed out that my 2008 was reporting pressures from torque extended GM pid. People indicated that it didn't work for them but I don't remember when the "pid challenge" was accepted BUT I do know that you (tjbaker57) provided me with the more "accurate" output formula. One thing that I haven't done is compare the output to the launch data reader. Related, can one have multiple odb's connected / daisy chained in some fashion? sorry for the "side car".

ADDED: I see a splitter cable can be had.