HVAC Issue

[09_BLK GMC]

Hello,
So first off hopefully this is the right section for these questions. Secondly I have done alot of searching with no real solution.

I have a 2011 Tahoe LS with Manual control with dual temp

I'm having problems with my AC canister underhood (sorry forgot what it was called) freezing up during AC during the summer which causes blockage of airflow in the cabin. I'm also having the same problem with the defrost. I shut them off so the cannister can defrost to run my AC/Defrost another little while before I have to do it again. Blend doors are currently not my issue as air flow goes where I have the dial set to. This is starting to really get on my nerves Lol! Any help on what it may be would be great!! Thank you!!

 

[wjburken]

Hello,
So first off hopefully this is the right section for these questions. Secondly I have done alot of searching with no real solution.

I have a 2011 Tahoe LS with Manual control with dual temp

I'm having problems with my AC canister underhood (sorry forgot what it was called) freezing up during AC during the summer which causes blockage of airflow in the cabin. I'm also having the same problem with the defrost. I shut them off so the cannister can defrost to run my AC/Defrost another little while before I have to do it again. Blend doors are currently not my issue as air flow goes where I have the dial set to. This is starting to really get on my nerves Lol! Any help on what it may be would be great!! Thank you!!

I would reach out to @UmmScott with this question.

 

[09_BLK GMC]

I would reach out to @UmmScott with this question.

Thank you!!

@UmmScott
Hello Scott, you think you can help me out?

 

[UmmScott]

If its freezing up, we really need a good quality gauge at least on the low side of the system.

Thats called the accumulator (referencing the canister you're mentioning)

Im not 100% sure on a 2011 model but im pretty sure its still a clutch cycling system. If so, then we really need to know the low side pressure of the system before going further. Theres not much else i can do without knowing this yet.
Also, being a 2011 model even tho you have manual temp controls, it may also be in control of freeze up issues. Ill have to look into that.

But really...cant really go further without knowing the running system pressures on the high and low sides. Could be a number of things. Overcharged, undercharged, weak compressor, stuck open rear AC expansion valve, high head pressure, failed closed clutch cycling switch...just to name some things.

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[09_BLK GMC]

If its freezing up, we really need a good quality gauge at least on the low side of the system.

Thats called the accumulator (referencing the canister you're mentioning)

Im not 100% sure on a 2011 model but im pretty sure its still a clutch cycling system. If so, then we really need to know the low side pressure of the system before going further. Theres not much else i can do without knowing this yet.
Also, being a 2011 model even tho you have manual temp controls, it may also be in control of freeze up issues. Ill have to look into that.

But really...cant really go further without knowing the running system pressures on the high and low sides. Could be a number of things. Overcharged, undercharged, weak compressor, stuck open rear AC expansion valve, high head pressure, failed closed clutch cycling switch...just to name some things.

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Damn, that is alot of stuff that could be the problem. Ill get that info and post up. Thank you!

 

[UmmScott]

Damn, that is alot of stuff that could be the problem. Ill get that info and post up. Thank you!

If you're determined to get the operating pressures... please study up or get someone local to help you test it.
I mean, you can go and buy a manifold test set but alot of guys who dont know the ins/outs of AC end up causing more issues.

I am here to help tho as best i can!

Does the rear AC unit work correctly?
How long have you owned the vehicle? Has the ac system ever been charged up or had history of being charged or tested?


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[09_BLK GMC]

If you're determined to get the operating pressures... please study up or get someone local to help you test it.
I mean, you can go and buy a manifold test set but alot of guys who dont know the ins/outs of AC end up causing more issues.

I am here to help tho as best i can!

Does the rear AC unit work correctly?
How long have you owned the vehicle? Has the ac system ever been charged up or had history of being charged or tested?


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I appreciate it, Thank you!

To answer your questions I have owned it since new and have never been serviced. The rear AC system appears to work fine. I did notice the rear passenger AC piping there aswell sweats/defrosts and leaves a puddle of water when I park the truck the same way as the front.

 

[UmmScott]

I appreciate it, Thank you!

To answer your questions I have owned it since new and have never been serviced. The rear AC system appears to work fine. I did notice the rear passenger AC piping there aswell sweats/defrosts and leaves a puddle of water when I park the truck the same way as the front.

Thats good info.

Here is a test i would do. Start car, turn AC on and controls to the coldest settings. Turn rear system OFF. Turn front system to coldest with the Lowest fan speed and turn recirc on. Let it run like this for 10 mins or more.
Wait until you see frost on the AC lines and accumulator. Keep an eye on the AC compressor clutch. Also put a thermometer in your ac vents.
During this test, when the frost starts to appear, the compressor clutch should begin to cycle off....then on...then off. Also, your vent temps shouldnt get much below 34 to 32F.

If....when doing this test, the compressor never shuts off. Take a blunt object and tap on the clutch cycling switch (on the accumulator and has 2 wires going to it)
If...when doing this, the comp cycles off ans stays off till the frost is all gone and vent temps warm up, then your cycling switch is sticking and causing your problems.

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[09_BLK GMC]

Thats good info.

Here is a test i would do. Start car, turn AC on and controls to the coldest settings. Turn rear system OFF. Turn front system to coldest with the Lowest fan speed and turn recirc on. Let it run like this for 10 mins or more.
Wait until you see frost on the AC lines and accumulator. Keep an eye on the AC compressor clutch. Also put a thermometer in your ac vents.
During this test, when the frost starts to appear, the compressor clutch should begin to cycle off....then on...then off. Also, your vent temps shouldnt get much below 34 to 32F.

If....when doing this test, the compressor never shuts off. Take a blunt object and tap on the clutch cycling switch (on the accumulator and has 2 wires going to it)
If...when doing this, the comp cycles off ans stays off till the frost is all gone and vent temps warm up, then your cycling switch is sticking and causing your problems.

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Ok, cool! Thank you!

 

[09_BLK GMC]

Thats good info.

Here is a test i would do. Start car, turn AC on and controls to the coldest settings. Turn rear system OFF. Turn front system to coldest with the Lowest fan speed and turn recirc on. Let it run like this for 10 mins or more.
Wait until you see frost on the AC lines and accumulator. Keep an eye on the AC compressor clutch. Also put a thermometer in your ac vents.
During this test, when the frost starts to appear, the compressor clutch should begin to cycle off....then on...then off. Also, your vent temps shouldnt get much below 34 to 32F.

If....when doing this test, the compressor never shuts off. Take a blunt object and tap on the clutch cycling switch (on the accumulator and has 2 wires going to it)
If...when doing this, the comp cycles off ans stays off till the frost is all gone and vent temps warm up, then your cycling switch is sticking and causing your problems.

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Also about the 2 wire plug, my accumulator doesn't have it. Unless I'm really overlooking something.

 

[UmmScott]

Also about the 2 wire plug, my accumulator doesn't have it. Unless I'm really overlooking something.
View attachment 233356

Ok... if you follow that large suction line back to the compressor, is there a 2 wire switch at all?

This system may not use the clutch cycling method like the 2006 and prior models do if there is no switch.
Your setup may be like that. So in this case, there are some other ways that GM uses to control it.
Some compressors have a control valve inside the compressor to keep the pressure above the freezing point.
Others use a sensor located inside the evaporator housing to monitor temperatures and when they get below freezing it will then cycle the compressor off. Yours is probably some form of this method

We need to figure out which one you have. Might need a scan tool that can access the HVAC module to see things further. I know you said you have manual Controls, but now a days its still computer controlled LOL!!

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[UmmScott]

Do you have control over the AC?

Like if you manually turn it off but leave the blower on, does it respond and turn off?

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[09_BLK GMC]

Ok... if you follow that large suction line back to the compressor, is there a 2 wire switch at all?

This system may not use the clutch cycling method like the 2006 and prior models do if there is no switch.
Your setup may be like that. So in this case, there are some other ways that GM uses to control it.
Some compressors have a control valve inside the compressor to keep the pressure above the freezing point.
Others use a sensor located inside the evaporator housing to monitor temperatures and when they get below freezing it will then cycle the compressor off. Yours is probably some form of this method

We need to figure out which one you have. Might need a scan tool that can access the HVAC module to see things further. I know you said you have manual Controls, but now a days its still computer controlled LOL!!

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Lol! True!
After searching the net it seems like the switch is closer to the compressor. Ill try and take a look later today and let you know.

 

[09_BLK GMC]

So just an update, I seem to have solved my issue. I changed out my cycling clutch switch. It was on the line close towards the compressor. I had both the defrost and AC running separately and didn't freeze up the accumulator. Ill let you guys know if it really fixes the issue on a longer drive.

 

[UmmScott]

Good to hear man. Keep us posted

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[09_BLK GMC]

Good to hear man. Keep us posted

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Thank you Sir! Will keep you guys posted!