A/C fades after 3 hours, starts cold next day, fades after 3 hours

[6716]

On a road trip this weekend I noticed that the A/C was not only not blowing cold after three hours on the road, but also the blower pressure seemed to be down. I noticed it Friday driving up north. Saturday was shorter driving, didn't notice it. Sunday it was noticeable driving home. Today it works like a charm in standard city driving.

Any ideas? I've got another -- longer -- road trip coming up in two weeks.

 

[The_Roadie]

AC coldness is typically not related to blower speed, but do you have the 5-speed manual fan control or the digital automatic? Have you ever lost a speed if you have the manual?

When you notice poor performance, check the temp by hand (or a digital thermometer if you have one) on the receiver/drier - the silver can on the passenger side of the firewall under the hood. See if it's chilly or warming up.

 

[6716]

Thanks for your response.

Yeah, it was strange to notice the lack of blower pressure ... the temp and the blower pressure shouldn't be related ... but there's a lot that I don't know.

I have the 5-speed manual, and I replaced the resistor pack (thanks to a thread on the OS) last summer because I had lost speeds.

I haven't noticed performance problems driving around town (it is my work vehicle, I drive a lot, but usually not more than an hour or so at a time). Shoot, it was blowing cold and strong today.

What will it mean if the receiver/drier is cold or warm when performance falls off? I will likely be in the middle of a road trip when it happens, so I'd like to have a couple of steps ready so I can troubleshoot / fix on the fly since the princess will be riding shotgun and she likes her A/C.

 

[Bravada]

Funny, I had the EXACT same thing happen to me. I was on a long trip and had reduced blower speed after a few hours. I stopped and my wife went to check into our hotel. As I sat there for a couple minutes, I noticed the engine temp was rising to about 220 instead of 210. Then it sounded like a bunch of ice broke up and the fan was blowing out full speed again.

So, after a few hours on the way home, it was doing this again. I turned off the A/C and ran just the vent for about 5 minutes. That seemed to take care of it. It was very humid, and condensation could have been freezing on the coils in the blower unit and restricting flow.

If anybody else has any idea what else this could be. Please let me know.

 

[6716]

Interesting.

Yeah, the A/C wasn't blowing hot, but the interior of the car was definitely hotter and the blower pressure was down.

Thanks for the tip on the running the vent. I'll try that.

 

[Mooseman]

There could be a few things going on. Have you tried pressure washing the condenser? The accumulation of dirt and bugs don't help. After that, when it does happen, stop and feel the accumulator(as Roadie explained) and also look at the compressor. Is the clutch spinning as fast as the pulley driving it? Does it look like it's slipping? If so, then this could be a clutch problem. Is it cycling on and off often? Then this would mean that you're low on refrigerant.

Another thing that is possible (but less probable) is that your low pressure switch is defective and not cycling the compressor thus freezing your evaporator and ice is blocking the flow of air. If that's the case, the accumulator would have frost on it and the clutch would not cycle at all. When it happens, turn off the A/C but leave the fan on. If the air flow increases and you're still getting cool air, then this could be your problem. Further troubleshooting would require a set of gauges to measure pressures.

 

[Bravada]

Another thing that is possible (but less probable) is that your low pressure switch is defective and not cycling the compressor thus freezing your evaporator and ice is blocking the flow of air. If that's the case, the accumulator would have frost on it and the clutch would not cycle at all. When it happens, turn off the A/C but leave the fan on. If the air flow increases and you're still getting cool air, then this could be your problem. Further troubleshooting would require a set of gauges to measure pressures.

This is likely what my problem is, and possibly the OP, since it is a reduced fan speed, but not an increased temp coming out of the vent. Do you think it is harmful to the system to leave it like this? We rarely drive the vehicle more than an hour at a time.

Thanks

 

[6716]

Well, shoot, Mooseman ... now I'm going to have to open the hood and learn something.

Where do you suppose I might find pictures and descriptions of the various A/C parts you've mentioned?

 

[Mooseman]

The manuals would be a good place to look at those (check my sig below). Also, rockauto.com shows pictures of individual parts.

When we try to assist people here in diagnosing problems, we tend to think that they do have some knowledge of auto mechanics and able to do some basic work. A/C is one of those things that is more advanced and if you are not familiar with some of these things, you may be better to just bring it to a qualified shop to work on it. At least you can give them a good description of the problem and maybe even show that you have some sort of knowledge so that they don't try to roll you over .

 

[6716]

Well, I'm not completely unskilled. I've done most of the TB basics (plugs, throttle body, thermostat, serpentine belt, blower resistor pack, pads and rotors).

Just too cheap to spend money on a manual, given the general quality of electronic content these days. And modest (on car repair forums, anyway).

Besides, the knowledge that I might just wreck something and/or cost myself a bunch more money than necessary makes it more interesting. Keeps the mind sharp, dontcha know.

 

[marce]

Hi GMTNATION I need help with 06 equinox 6 cly that is having same issue. cold air then ten minutes later hot turn it off cold and repeat pattern .Now i know this is TB/360 but my sis has Equinox Sooo can you direct me to a good site that has Knowledgeable members like yourselfs.I have tried to find by myself On a plus OS write up on resistor was great help! Done last weekend, lasted two days an 5 goes out w/burning smell doing the Harness this time (shoulda listened to Roadie). Any help appreciated Maggie

 

[Mooseman]

Well, I'm not completely unskilled. I've done most of the TB basics (plugs, throttle body, thermostat, serpentine belt, blower resistor pack, pads and rotors).

Just too cheap to spend money on a manual, given the general quality of electronic content these days. And modest (on car repair forums, anyway).

Besides, the knowledge that I might just wreck something and/or cost myself a bunch more money than necessary makes it more interesting. Keeps the mind sharp, dontcha know.

The manuals I have available for download aren't that bad, just not searchable or indexed. They do explain fairly well most repair jobs. No slight towards you on your mechanical knowledge. I was just thrown off a bit when you asked for pics and descriptions . But A/C diagnosis and repair does require equipment that is not in most DIY'er toolbox.

 

[Mooseman]

Hi GMTNATION I need help with 06 equinox 6 cly that is having same issue. cold air then ten minutes later hot turn it off cold and repeat pattern .Now i know this is TB/360 but my sis has Equinox Sooo can you direct me to a good site that has Knowledgeable members like yourselfs.I have tried to find by myself On a plus OS write up on resistor was great help! Done last weekend, lasted two days an 5 goes out w/burning smell doing the Harness this time (shoulda listened to Roadie). Any help appreciated Maggie

Well hi there! We welcome all GMT's. A/C problems are usually common across different models from the same brand. The stuff discussed earlier should be the same for yours, just that my manuals don't cover Equinox.

 

[6716]

Another thing that is possible (but less probable) is that your low pressure switch is defective and not cycling the compressor thus freezing your evaporator and ice is blocking the flow of air. If that's the case, the accumulator would have frost on it and the clutch would not cycle at all. When it happens, turn off the A/C but leave the fan on. If the air flow increases and you're still getting cool air, then this could be your problem. Further troubleshooting would require a set of gauges to measure pressures.

I think this is the problem. On a longer ride today it seemed like it was fading and I shut off the A/C and just ran the fan, and it ran cold for a few minutes. When that started to warm up I switched the A/C back on and it worked.

Beyond that, though, I'm trying to figure out how to see the clutch on the compressor ... seems like it's one of those things easier said than done.

Thanks for the info, and the work-around.

 

[SBUBandit]

Beyond that, though, I'm trying to figure out how to see the clutch on the compressor ... seems like it's one of those things easier said than done.

Look at the bolts on the flat front surface of the pulley. When you start the truck, with air off, you'll notice those aren't spinning even though the belt is spinning. clutch isn't engaged. Turn on the air. when the clutch engages you'll see that front plate start spinning. clutch engaged. Keep watching, and you'll notice it turns on and off once in a while.

 

[6716]

Look at the bolts on the flat front surface of the pulley. When you start the truck, with air off, you'll notice those aren't spinning even though the belt is spinning. clutch isn't engaged. Turn on the air. when the clutch engages you'll see that front plate start spinning. clutch engaged. Keep watching, and you'll notice it turns on and off once in a while.

Nice! I'll check that out right now.

 

[6716]

Keep watching, and you'll notice it turns on and off once in a while.

So ... you were just messin' with me, right? Wanted to see how long I would stand in the driveway looking into the engine compartment, waiting for the clutch to stop spinning?

'Cause it didn't. Not once, not a little bit.

System blew cold pretty well, the accumulator was good 'n cold, as were the silver-colored lines running to and from it.

But the clutch on the compressor just kept going and going.

 

[SBUBandit]

So ... you were just messin' with me, right? Wanted to see how long I would stand in the driveway looking into the engine compartment, waiting for the clutch to stop spinning?

'Cause it didn't. Not once, not a little bit.

System blew cold pretty well, the accumulator was good 'n cold, as were the silver-colored lines running to and from it.

But the clutch on the compressor just kept going and going.

LOL, no I really wasn't messing with you. I don't know exactly how it all works, but I'm pretty sure if it runs non stop it will eventually freeze up somewhere in the system. I know mine will cycle on and off over time. If it does it too fast its possible it doesn't have enough charge, but that must not be the problem. But I do believe its supposed to cycle on and off eventually. Maybe not till it gets pretty cold.

 

[neelskit]

So ... you were just messin' with me, right? Wanted to see how long I would stand in the driveway looking into the engine compartment, waiting for the clutch to stop spinning?

'Cause it didn't. Not once, not a little bit.

System blew cold pretty well, the accumulator was good 'n cold, as were the silver-colored lines running to and from it.

But the clutch on the compressor just kept going and going.

The compressor clutch will cycle on and off based on a number of factors: high/low side pressure switches, engine load, temperature commanded from HVAC controls, and engine/trans temperature. Basically, the PCM controls the compressor clutch engagement based on feedback from the BCM, HVAC Control Module, and various sensors. In a system that is operating properly, with the correct refrigerant charge, I would expect the compressor to stay engaged at idle on a hot day.

 

[6716]

The compressor clutch will cycle on and off based on a number of factors: high/low side pressure switches, engine load, temperature commanded from HVAC controls, and engine/trans temperature. Basically, the PCM controls the compressor clutch engagement based on feedback from the BCM, HVAC Control Module, and various sensors. In a system that is operating properly, with the correct refrigerant charge, I would expect the compressor to stay engaged at idle on a hot day.

Thanks for the tip.

At the parts store I did two things: first, disconnected the A/C low pressure switch (which caused the compressor to stop ... though I suppose (but i don't rightly know for sure) that was to be expected, and not new information), and second, checked the low side pressure at the accumulator, and it was at 45 psi.

I'm starting to look at picking up a scan tool, since a lot of the troubleshooting for A/C electric seems to use that.

 

[neelskit]

Thanks for the tip.

At the parts store I did two things: first, disconnected the A/C low pressure switch (which caused the compressor to stop ... though I suppose (but i don't rightly know for sure) that was to be expected, and not new information), and second, checked the low side pressure at the accumulator, and it was at 45 psi.

I'm starting to look at picking up a scan tool, since a lot of the troubleshooting for A/C electric seems to use that.

Was that pressure reading with the compressor running or static? If you've downloaded the service manuals, look in the HVAC file, page 10 for the pressure table. Also, be careful using the "cheapie" low-side only gauges at the parts store. They only give you half the story. To properly troubleshoot any A/C system you need accurate readings of BOTH the high and low side of the system static and running.

As far as buying a scan tool, only a Tech II will be able to communicate with the HVAC module and the BCM. A generic scan tool won't help you troubleshoot the HVAC system.

 

[6716]

Was that pressure reading with the compressor running or static?

As far as buying a scan tool, only a Tech II will be able to communicate with the HVAC module and the BCM. A generic scan tool won't help you troubleshoot the HVAC system.

Compressor running only, low side only, using the gauge on a "returned as defective" A/C re-charge kit (I didn't add any refrigerant).

How about this tool: OBDCOM Diagnostic Systems for ALL vehicles

 

[6716]

How about this tool: OBDCOM Diagnostic Systems for ALL vehicles

Actually, that tool won't do the trick on A/C diagnostic per info@obdcom.

 

[neelskit]

Compressor running only, low side only, using the gauge on a "returned as defective" A/C re-charge kit (I didn't add any refrigerant).]

Apparently an A/C manifold gauge set at Harbor Freight is under $50. Following the pressure test steps found in the service manual in the "HVAC" file. Do a search for service manuals to download them...