NEED HELP Idle Hunting While Using Air Conditioning

therealsethallen

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Sep 20, 2015
501
Western Mass.
So ye olde 4.2 is having some slight idle issues. When I start it up, with the A/C on, the truck will sit at 1k revs as opposed to the normal 600 at least until I drop it into gear. If I let it idle in park with the A/C turned on, it will idle up to about 1100 then back down to the normal 600. It'll do this every couple of minutes. Then, while driving it does the same thing between 1k and 2k RPM. It has never stalled. I cleaned the throttle body last night (it wasn't dirty) and that did nothing. We've had a string of 85-90 degree days here and I've found myself not wanting to use the A/C because of this. I've checked for vacuum leaks and have found none.

When I got the truck back after the engine replacement, all the lights have had a slight flicker, and the volt meter on the dash is pegged right at half. I'm wondering if this whole issue is because having the climate control on is draining the battery. It's an occasional thing though, much like the happenings wit the lights.

I'm totally stumped!
 

Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
Did you disconnect the battery or pull the PCM fuses after cleaning the throttle body for 30 minutes?
 

mrrsm

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Symptomatically... My first guess would be a sticking or dirty or failing Electronic Throttle body. However my second guess is that your AC Compressor is beginning to let go... The lurching is generally caused by the internal resistance pulling against the Serpentine belt which you can observe yourself by watching the Belt Tensioner bouncing hard to absorb the drag on it, watching carefully as someone is turning the AC on and off for a few 10-15 second intervals.

The "Hunting" response could be the PCM getting 'caught from ambush' and trying to stabilize the load on the engine with fuel trim adjustments. Sometimes, as the the vehicle gets under way... the higher RPM may seem unusually laboured while shifting through the gears...fighting the drag caused by the resistance from the AC Compressor.

Likewise you can further investigate the problem by removing the Serpentine Belt...hopefully your battery is fully charged and robust with "AMPle" Power (pun intended) ...and trying to start the engine and elevate the RPM just a bit and suddenly letting off of the gas to see if the surge returns. Unfortunately the Throttle Body in the Atlas Engine is a Solid State, Unified unit... without a separate TPS sub-component or provide a way to to investigate a failing Butterfly Control Motor.

The third possible with the flickering lights could be bearings in the Alternator.
 
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MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
Does the rpm change happen when the compressor clutch engages/disengages?
 

littleblazer

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Jul 6, 2014
9,265
So other than this hunting ant other drivability issues?

Also Is the AC cold or cool?
 

therealsethallen

Original poster
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Sep 20, 2015
501
Western Mass.
So other than this hunting ant other drivability issues?

Also Is the AC cold or cool?

No other issues. The A/C is decent but it takes a bit to really cool down if it's over 80 outside, and even then I have to crank it. It was like this last summer and I chalked it up to needing a recharge. But it was professionally recharged less than a month ago.
 

littleblazer

Member
Jul 6, 2014
9,265
Wonder if it's maybe low and it's hunting because of that. Another vehicle of mine raises the idle when it cycles alot so it doesn't stall.
 

therealsethallen

Original poster
Member
Sep 20, 2015
501
Western Mass.
Wonder if it's maybe low and it's hunting because of that. Another vehicle of mine raises the idle when it cycles alot so it doesn't stall.

It has the correct charge. It's the 1.89lbs that the manual calls for. Though it may be. It hasn't affected anything else and the air does work.
 

MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
Do you have the means to read engine data? I'd want to know the desired rpm vs actual rpm when it's acting up.
 

steveO

Member
Apr 6, 2012
91
No other issues. The A/C is decent but it takes a bit to really cool down if it's over 80 outside, and even then I have to crank it. It was like this last summer and I chalked it up to needing a recharge. But it was professionally recharged less than a month ago.

I suspect you have other issues with the A/C causing the compressor to kick out.
I have never had mine charged and it's a 2002 and works great so if you lost a charge my bet is it has a leak or some other issue within the system itself.
Take back to the guy who worked on it or a reputable A/C pro. A simple thing like a leaking Schrader valve might be all it is if your lucky.

Edit: Whoops wrong fitting
 

therealsethallen

Original poster
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Sep 20, 2015
501
Western Mass.
Well, the engine was replaced. It had to be evacuated and recharged when that was done. But I had to charge it last year and it was pretty marginal then, but I never had this idle issue.
 

steveO

Member
Apr 6, 2012
91
Well, the engine was replaced. It had to be evacuated and recharged when that was done. But I had to charge it last year and it was pretty marginal then, but I never had this idle issue.

Only other thing I can think of is the bearing is going on the compressor and the coil is overheating. If you see black tarry stuff behind the compressor it is likely the cause. I had a failure of the bearing that caused similar symptoms as well.
Luckily I never had to mess with the closed system.
I had to replace the compressor bearing and the clutch which was part of a rebuilt clutch I purchased which included the coil.
The coil was damaged due to the friction and heat from the bad bearing. Didn't make much noise to indicate the bearing was bad but when you garbed the pulley with the belt off it was obvious.
 

therealsethallen

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Sep 20, 2015
501
Western Mass.
@MAY03LT I got the rig plugged into a Verus (Snap-On doesn't have an update for the 9-7 without buying a crazy expensive update, so I tricked it into thinking its an 05 Rainer) At idle with the air off it sits between 600-610. Desired idle is 600rpm. When the air is on it gets up to 1100 at the highest point and drops to 570 at the lowest point. It has not stalled.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I think it's cycling more than it should. You have the air blasting on max? Might be low. But even when cycling, it shouldn't vary the idle by that much. Both of mine will vary about 200 for a second or so. Have you tried resetting the PCM by disconnecting the battery (or PCM fuses) for 30 min.? It's worth a shot. I'm also thinking fuel pressure.

On another note, your fan doesn't look like it's spinning very hard, more like freewheeling.
 

mrrsm

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Great Video and associated observations and comments. This is very helpful seeing the activity up close and personal. I cannot tell whether the AC Compressor is cycling on and off by someone following your instructions to act as your Proxy in the Cab... or if this is its present behaviour on its own. While cycling on and off... I did NOT notice that the engine was especially labouring with the normal drag imposed by the compressor engaging and it did NOT appear in any jeopardy of stalling. Air Conditioning Compressors compress Vapours and NOT Liquids as Liquids are incompressible. Yet... the by-product of this activity is to compress the Refrigerant Vapour enough while removing the Latent and Sensible Heat picked up during the endlessly circulating refrigerant gas that is absorbed via the Evaporator from inside of the Cab...and causes the Vapour to experience a "Change of State" from a HydroChloroFluoroCarbon (HCFC) Gas...into a Freon like Liquid.

If the HVAC system in the vehicle has TOO Much Refrigerant... what will happen is that there will be so much excess liquid flowing out of the Compressor and back through the Condensing unit...that the Compressor Vanes will encounter Pure Liquid...and "SLUG" itself to a halt. Since compressors MUST be protected from this event or be destroyed in the process...there is usually a protective Electrical High Pressure Sensor... that will invoke immediately in order to shut of the Electro-Magnetic Clutch and disconnect the driving force of the Serpentine Belt and AC Clutch Pulley to stop from destroying the Compressor. This will happen...ad infinitum ...until the Compressor is damaged to the point of failure.

Conversely...as suggested above by @littleblazer and repeated by @Mooseman ...if the system is Under Charged... the Low Pressure Cut Off Switch will disengage the Electro-Magnetic Clutch in the same manner...but the reason for doing this is that the PAG Lubricant cannot move through the system enough to Lubricate the Compressor...and it will die from lack of lubrication if an insufficient amount of refrigerant is present in the system to move the PAG Oil around.

The only definitive manner to determine which of these phenomena are at play is to attach an Automotive AC Manifold Gauge Set to to the system (Red Hose to HP...Blue Hose to LP using common 'Quick Disconnect" fittings on the hoses) and read the pressures on the high and low sides at the same time... The compound gauge on the left measures both Vacuum and "Blue" Low Pressure Vapour...and the "Red" High Pressure Gauge on the right reads Higher Liquid Line Pressure...or what we call "Head Pressure". Doing this will reveal what is happening on both sides of the system and make diagnosing the problem quite a bit easier to perform. You should determine what your normal range of pressures for your system are supposed to look like before setting up the equipment and running the test. On rare occasions...either the Low Pressure Switch or the High Pressure Switch in the Compressor may be the faulty component.

Hope this is Helpful...

EDIT:

The Low Pressure Switch IS on of those rare, replaceable Auto AC Components that is both relatively inexpensive AND easy to R&R. The reason for this is because the in-line port that holds it has a Schrader Valve nested inside. The LPACS (generally made of Gray Plastic or Aluminium) is designed with a push-pin inside that once the sensor is threaded onto the outside of the Low, Return side line port... it seals the refrigerant by means of an internal HVAC "O"-Ring and depresses the Schrader enough to allow the Refrigerant access to the internal pressure plate so the "sensor...can sense".

More often than not...these get over-tightened to point of cracking in the body of the plastic hex nut and the refrigerant will vacate the system. The R&R is easily done by disconnecting the two wire connector and simply un-screwing the lower cap off of the line. It will be necessary to have a small screwdriver handy to quickly reset the the Scrader pin inside in case it gets stuck open and atmospherically vent R-134A... so if you decide to do this repair...be ready for the tell-tale hiss. B4 you install its replacement... I recommend coating the inside of the threads and "O"-Ring with a little bit of "NYLOG".
 
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therealsethallen

Original poster
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Sep 20, 2015
501
Western Mass.
@Mooseman @MRRSM I had the air cranked, nobody with me and got out for the video. I'll add, on cold starts there's a little bit of a whine from the fuel tank, my presumption is the fuel pump is on it's way out, slowly but surely. It goes away after some time and doesn't happen at idle. It's even occasional on cold starts. I think the pump is just old and tired and ready do die. The thermostat is also getting lazy, I ordered one from Amazon yesterday and a Gallon of Dexcool.

As it so happens, I was investigating the charging system so I had the ground strap off the battery for a good half hour, and managed to lose a bolt for the battery cover. Afterwards this video was created. I will say that the uphill sort of chugging and idle hunting while in gear seems to have ceased. Today was one of the warmest days we've yet had here in New England at 87 Fahrenheit (That's 30C to you my northern bro) Parked idling for about fifteen minutes with the air going a few clicks down from highest, on recirculate it felt pretty good. On the highway at 60mph it cools quite well and I've noticed no drivability issues. The strange thing is this doesn't seem to happen any other time aside from when sitting at idle.
 

mrrsm

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therealsethallen

Original poster
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Sep 20, 2015
501
Western Mass.
@MRRSM Unfortunately I cannot do that. My truck is a 2005, and one of the year changes for that truck was a non serviceable in tank filter that's part of the pump assembly. My next goal is to replace the pump but that's not in the budget at the moment.
 
Last edited:

Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
If the A/C is cranked, warm/hot out and it's idling, it shouldn't be cycling like that. If it's blowing really cold, being undercharged, may have the opposite effect of overcooling because the lower the pressure, the cooler the air. I have seen some evaporators freeze up because of that to the point that it could not let air pass through. Either a set of gauges or a trip to a shop would confirm this.

Could very well be that the pump is slowly dying. And that the symptoms seem to disappear with the whine makes it a suspect.
 
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therealsethallen

Original poster
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Sep 20, 2015
501
Western Mass.
It's nearly 90 today and I parked it in the sun. I just left a friend's house, got in turned it on an drove throughout town comfortably.

Could very well be that the pump is slowly dying. And that the symptoms seem to disappear with the whine makes it a suspect.

I've got a sneaking suspicion it is causing my odd idle as whole. It's not a rough idle like so many people with dirty throttle bodies post about. I'm leaning towards pump failure for another reason, when the old engine started having valve issues, I had to drive it still and it hard started when warm putting a little extra stress on the pump. I'm going to run some Lucas or Techron through it and see if that helps.

The Low Pressure Switch IS on of those rare, replaceable Auto AC Components that is both relatively inexpensive AND easy to R&R.

I'm very possibly going to take a stab at that just for laughs. I'll grab a handful of them from the pull-a-part next time I'm there. No use in a new one if it's not the end-all problem.
 

mrrsm

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If the A/C is cranked, warm/hot out and it's idling, it shouldn't be cycling like that. If it's blowing really cold, being undercharged, may have the opposite effect of overcooling because the lower the pressure, the cooler the air. I have seen some evaporators freeze up because of that to the point that it could not let air pass through. Either a set of gauges or a trip to a shop would confirm this.

Could very well be that the pump is slowly dying. And that the symptoms seem to disappear with the whine makes it a suspect.

I like @Mooseman 's Perfect Description here... and if I may... I'll add three pictures to show just how completely frozen over the evaporator under the dashboard inside the cab can really become... and elaborate on the technical reasons for why this can occur:

frozen-ac.jpg

iu


Instead of a Fixed Orifice...THIS last image shows an Evaporator Unit which employs a TXV (Thermostatic eXpansion Valve) that tends to be more forgiving of variable amounts of charges of refrigerant. Note the FILTHY and FROZEN AIR FILTER ON THE RIGHT SIDE!
IMG_2303x.jpg


Now even though these images are of Residential HVAC "A" Frame- like Evaporator Coils that have frozen over... their value for demonstration purposes is clear... If you observe the lower section of the first image...you can see where the Copper "L" Liquid Line ends at the Brass Coupling... and what should be a group of very fine capillary copper tubes branching out to the left and right sides that feed larger copper tubes in the angled finned areas. But as you can observe...The entire thing from the point of that Brass fitting onward... is obscured and has become just a solid block of Ice.

Just inside of that Brass Fitting is a Fixed Sized Orifice that ordinarily allows the hot, liquid refrigerant to branch out uniformly at a prescribed rate...and when the liquid reaches the larger tubes...it expands gradually as a mixture of gas and liquid at the entry point... and by the time it reaches the top of each side.,..it has fully expanded into refrigerant vapour. The energy required to make this evaporation "Change of State" to take place is "stolen" right out of the air that the AC Blower in the cab is pushing through and over the coils...and the consequence of that is that the air temperature drops and any water vapour being carried inside the air stream...collects on the Evaporator fins (often referred to as being "Beer Can Cold") and drops down into a Drain Tube to gravity feed outside under the vehicle and pool on the ground, After that...things get nice and cool and de-humidified inside the cab...as long as everything is working properly.

Ideally... Air Conditioners work best when the temperature of the evaporator coils does not drop below 38-40 degrees Fahrenheit . But if the Refrigerant Charge is Too Low... what will happen is that the Hot Liquid inside the Liquid Line will be so scarce, that as the liquid approaches the evaporator... it will prematurely "FLASH OVER" inside the entry port of the Evaporator... drawing the ambient heat from the air stream so rapidly at sub-freezing temperature... and any moisture left in the air stream will instantly freeze solid on the internal coils and fins of the Evaporator. When enough of the moisture collects in between... the Ice will simply block off the flow of the air entirely... and so what looks like it should make the air inside the cab REAL COLD... will become nothing more than a FROZEN PLUG. And now... the only way out of this Freezing Purgatory... is to isolate the leak(s) and repair them... and then charge the system gradually... after the Ice Block melts completely and the Evaporator returns to normal.

If it comes down to cases and the Compressor requires a change out... just a word of practicality. There are only Two Kinds of Compressors to consider using:

----== The Ones that WORK...and the Ones that DON'T==----

The Best:
(1) AC-Delco
(2) Delphi

The Worst:
(3) All the Rest of the Cheap, Inexpensive New and Rebuilt Ones that will FAIL in 6 Weeks!
 
Last edited:

therealsethallen

Original poster
Member
Sep 20, 2015
501
Western Mass.
I like @Mooseman 's Perfect Description here... and if I may... I'll add three pictures to show just how completely frozen over the evaporator under the dashboard inside the cab can really become... and elaborate on the technical reasons for why this can occur:

frozen-ac.jpg

iu


Instead of a Fixed Orifice...THIS last image shows an Evaporator Unit which employs a TXV (Thermostatic eXpansion Valve) that tends to be more forgiving of variable amounts of charges of refrigerant. Note the FILTHY and FROZEN AIR FILTER ON THE RIGHT SIDE!
IMG_2303x.jpg


Now even though these images are of Residential HVAC "A" Frame- like Evaporator Coils that have frozen over... their value for demonstration purposes is clear... If you observe the lower section of the first image...you can see where the Copper "L" Liquid Line ends at the Brass Coupling... and what should be a group of very fine capillary copper tubes branching out to the left and right sides that feed larger copper tubes in the angled finned areas. But as you can observe...The entire thing from the point of that Brass fitting onward... is obscured and has become just a solid block of Ice.

Just inside of that Brass Fitting is a Fixed Sized Orifice that ordinarily allows the hot, liquid refrigerant to branch out uniformly at a prescribed rate...and when the liquid reaches the larger tubes...it expands gradually as a mixture of gas and liquid at the entry point... and by the time it reaches the top of each side.,..it has fully expanded into refrigerant vapour. The energy required to make this evaporation "Change of State" to take place is "stolen" right out of the air that the AC Blower in the cab is pushing through and over the coils...and the consequence of that is that the air temperature drops and any water vapour being carried inside the air stream...collects on the Evaporator fins (often referred to as being "Beer Can Cold") and drops down into a Drain Tube to gravity feed outside under the vehicle and pool on the ground, After that...things get nice and cool and de-humidified inside the cab...as long as everything is working properly.

Ideally... Air Conditioners work best when the temperature of the evaporator coils does not drop below 38-40 degrees Fahrenheit . But if the Refrigerant Charge is Too Low... what will happen is that the Hot Liquid inside the Liquid Line will be so scarce, that as the liquid approaches the evaporator... it will prematurely "FLASH OVER" inside the entry port of the Evaporator... drawing the ambient heat from the air stream so rapidly at sub-freezing temperature... and any moisture left in the air stream will instantly freeze solid on the internal coils and fins of the Evaporator. When enough of the moisture collects in between... the Ice will simply block off the flow of the air entirely... and so what looks like it should make the air inside the cab REAL COLD... will become nothing more than a FROZEN PLUG. And now... the only way out of this Freezing Purgatory... is to isolate the leak(s) and repair them... and then charge the system gradually... after the Ice Block melts completely and the Evaporator returns to normal.

If it comes down to cases and the Compressor requires a change out... just a word of practicality. There are only Two Kinds of Compressors to consider using:

----== The Ones that WORK...and the Ones that DON'T==----

The Best:
(1) AC-Delco
(2) Delphi

The Worst:
(3) All the Rest of the Cheap, Inexpensive New and Rebuilt Ones that will FAIL in 6 Weeks!

Fortunately I've got the compressor that came with my used engine. The R&R isn't hard. But, there's a handfull small of things that I need to do first before the luxuries.
 
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therealsethallen

Original poster
Member
Sep 20, 2015
501
Western Mass.
So, I changed the belt tensioner today to see if that might have something to do with it. It was pretty bad. While I was doing that, I noticed the water pump was a little loose. I'm doing my thermostat on Wednesday, but I was wondering if the water pump may also be failing. There's some noise while the engine is running. I am not sure what water pump was used when the engine was replaced. See video. For whatever reason this isn't really documented in video anywhere on the site.

 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I've seen Cardone pumps fail fairly fast, as well as Gates. I can't see the video right now but if it's that loose beyond your comfort level, I'd change it for peace of mind. I doubt it's the cause of the erratic idle though.
 
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therealsethallen

Original poster
Member
Sep 20, 2015
501
Western Mass.
I've seen Cardone pumps fail fairly fast, as well as Gates.

My mechanic told me he will not install a Gates pump. He doesn't want to warranty it in a week when it fails. His words. I got the ACDelco pump. The spring on the tensioner is shot so it's bouncing around a bit. I bought all ACDelco Parts, Thermostat, Water Pump, Tensioner and belt.
 

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