2011 Tahoe AC Cuts Out

[Jon Miles]

I am turning to the experts here because I'm banging my head against the wall with the ac system in the truck.
Some backstory:
Had an ac leak at the rear evaporator (no surprise with the age of the truck).
Replaced the rear lines and evaporator = leak gone.
Had the system recharged to spec'd pressures - still no leak.
Replaced the high pressure sensor, ac compressor relay, ambient temp sensor and the evap temp sensor.
Intermittent cooling persisted so I pulled the relay and jumped it. Compressor comes on and stays on so I replaced the relay.
AC runs cold for 15 mins or so after start up and then goes warm. Occasionally, it will come back on but it didn't seem to have method to its madness.
Until I noticed that when the volts drop off to 12~ at highway speeds, that is when the ac compressor kicks off and the air goes to ambient temp from the vents.

My troubleshooting mind points me to the compressor clutch but I really wanted to see what you all thought...

Thanks in advance.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me in this area will chime in.

 

[j91z28d1]

is it an automatic ac or a manual?

it's hard to do anything with a automatic ac without a good scanner you can see the ac request from the ecm

 

[swathdiver]

I am turning to the experts here because I'm banging my head against the wall with the ac system in the truck.
Some backstory:
Had an ac leak at the rear evaporator (no surprise with the age of the truck).
Replaced the rear lines and evaporator = leak gone.
Had the system recharged to spec'd pressures - still no leak.
Replaced the high pressure sensor, ac compressor relay, ambient temp sensor and the evap temp sensor.
Intermittent cooling persisted so I pulled the relay and jumped it. Compressor comes on and stays on so I replaced the relay.
AC runs cold for 15 mins or so after start up and then goes warm. Occasionally, it will come back on but it didn't seem to have method to its madness.
Until I noticed that when the volts drop off to 12~ at highway speeds, that is when the ac compressor kicks off and the air goes to ambient temp from the vents.

My troubleshooting mind points me to the compressor clutch but I really wanted to see what you all thought...

Thanks in advance.

Welcome to the forum Jon. Do you know anyone with a bi-directional scan tool like a Snap-On or Tech-2? They can see any internal trouble codes for this and or the reasons why the compressor kicks off and a lot of other things for diagnosis. We have a Tech-2 owner's map where you can see if anyone on here lives near you that has one.

@91RS @rockola1971

 

[mikez71]

Intermittent cooling persisted so I pulled the relay and jumped it. Compressor comes on and stays on so I replaced the relay.
AC runs cold for 15 mins or so after start up and then goes warm. Occasionally, it will come back on but it didn't seem to have method to its madness.
Until I noticed that when the volts drop off to 12~ at highway speeds, that is when the ac compressor kicks off and the air goes to ambient temp from the vents.

Does the A/C kick off with relay jumped at highway speed (voltage)?

There is a setting in hptuners "airflow system minimum voltage" which happens to be set at 12.0 volts...

 

[OR VietVet]

"Until I noticed that when the volts drop off to 12~ at highway speeds, that is when the ac compressor kicks off and the air goes to ambient temp from the vents.

My troubleshooting mind points me to the compressor clutch but I really wanted to see what you all thought..."

Voltage drops to 12 volts where? The clutch needs correct voltage to work and if is loosing that voltage, then the clutch will not engage and if you replace the clutch, you still have the voltage problem. What are the pressures in the system when it is working? System may be freezing up. I am unsure that all your info is complete. Not accusing, just stating uncertainty. Why did you not replace the orifice and the accumulator? How long on the vacuum pump?

 

[Jon Miles]

is it an automatic ac or a manual?

it's hard to do anything with a automatic ac without a good scanner you can see the ac request from the ecm

j9 - It's an auto ac system but I hardly use the feature, just run it manual.
Agreed - A buddy has a Snap-On scanner. I'll try and hook up with him later this week.

 

[Jon Miles]

Does the A/C kick off with relay jumped at highway speed (voltage)?

There is a setting in hptuners "airflow system minimum voltage" which happens to be set at 12.0 volts...

Mike, the short answer is no, it does not cut out. Did exactly that last week when it was 90 degrees. 45 mins into an hour drive, the airflow through the vents slowed down drastically. Pulled over, popped the hood and the dryer was frosted over. Pulled the jumper wire and replaced the relay. Airflow improved and the air was frigid from the vents.

 

[Jon Miles]

"Until I noticed that when the volts drop off to 12~ at highway speeds, that is when the ac compressor kicks off and the air goes to ambient temp from the vents.

My troubleshooting mind points me to the compressor clutch but I really wanted to see what you all thought..."

Voltage drops to 12 volts where? The clutch needs correct voltage to work and if is loosing that voltage, then the clutch will not engage and if you replace the clutch, you still have the voltage problem. What are the pressures in the system when it is working? System may be freezing up. I am unsure that all your info is complete. Not accusing, just stating uncertainty. Why did you not replace the orifice and the accumulator? How long on the vacuum pump?

OR - Sorry for the lack of info and appreciate you chiming in...At the volt gauge on the dash, I did not put a volt meter to the compressor as yet. When functioning, the low is 35psi +/- and the high is 175-190.
I had the system evacuated before I replaced the rear lines and evaporator. I did replace the orifice tube at that time - forgot to mention that replacement. Left the accumulator alone.
When I took it back to be refilled, it was on the vacuum for about an hour.

 

[Jon Miles]

Welcome to the forum Jon. Do you know anyone with a bi-directional scan tool like a Snap-On or Tech-2? They can see any internal trouble codes for this and or the reasons why the compressor kicks off and a lot of other things for diagnosis. We have a Tech-2 owner's map where you can see if anyone on here lives near you that has one.

@91RS @rockola1971

Thanks Swath.
I've been lurking for awhile but this is my first post...the amount of knowledge here is impressive and I value that greatly!
Yes, a friend has a Snap-On scan tool. Hoping to get over to see him in the next few days.

 

[OR VietVet]

How old is accumulator? You open ANY a/c system and if is 2-3 years old or older, IMO, you replace that accumulator. Not doing so, again IMO, is like doing an engine oil change without the oil filter.

 

[Jon Miles]

How old is accumulator? You open ANY a/c system and if is 2-3 years old or older, IMO, you replace that accumulator. Not doing so, again IMO, is like doing an engine oil change without the oil filter.

Appreciate your input, OR. I'm no mechanic, I just have come to enjoy puttering around on my Tahoe and saving some $.

Aside from the accumulator/dryer replacement, I read on another post here about the compressor coil and clutch gap. Could either be affected by the voltage drop regulated by the rvc sensor to +/- 12v?

 

[rockola1971]

Appreciate your input, OR. I'm no mechanic, I just have come to enjoy puttering around on my Tahoe and saving some $.

Aside from the accumulator/dryer replacement, I read on another post here about the compressor coil and clutch gap. Could either be affected by the voltage drop regulated by the rvc sensor to +/- 12v?

I think you are barking up the wrong tree with the voltage. I wouldnt trust what the gauge is showing. You stated in a previous post " Sorry for the lack of info and appreciate you chiming in...At the volt gauge on the dash, I did not put a volt meter to the compressor as yet. When functioning, the low is 35psi +/- and the high is 175-190."
Im guessing its substantially warmer than 80deg outside where you are and if it is then your pressures should be subtantially higher. The pressures should be checked with your system manually running on high fan (max cooling) both front and rear a/c and allow 10 minutes to stabilize. It appears your system charge is low. I would expect a min of 40-45psi if not higher on the low side and 200psi+ on the high side. Attached is a temp vs pressure chart. Your symptoms are standard for a system that is undercharged. The question is did it get undercharged or was it properly charged and still has a leak.

Not too mention a frosted over dryer/accumulator is a tattletale for a undercharged system. Your evaporator is icing over also because the refrigerant pressure is not above 32deg. Your humidity in the vehicle is freezing instead of evaporating at the evaparator which is what happens on a undercharged system (home a/c, refrigerator/freezer, window unit and even auto a/c).

 

[mikez71]

Mike, the short answer is no, it does not cut out. Did exactly that last week when it was 90 degrees. 45 mins into an hour drive, the airflow through the vents slowed down drastically. Pulled over, popped the hood and the dryer was frosted over. Pulled the jumper wire and replaced the relay. Airflow improved and the air was frigid from the vents.

In that case it wouldn't seem to be a clutch issue.

 

[j91z28d1]

Does the A/C kick off with relay jumped at highway speed (voltage)?

There is a setting in hptuners "airflow system minimum voltage" which happens to be set at 12.0 volts...

I would look into this.. while the voltage on the dash will definitely be different than actual voltage at the battery or the clutch. but that dash voltage is from the body control module and it's probably very close to the same the hvac measures or the bcm might just report the voltage over can bus to the hvac, I think that's what it does to the dash reading. either way if hp tuners is correct and it sees under 12v it might not request the ac on.

if you get your buddy's scanner, under the hvac module, try to find a voltage reading and the ac request data. if request is no check the voltage is below the cut off point. if it is, I'd clean all the ground and maybe replace the battery cables. they seem to be a pretty common issue.

 

[Jon Miles]

I think you are barking up the wrong tree with the voltage. I wouldnt trust what the gauge is showing. You stated in a previous post " Sorry for the lack of info and appreciate you chiming in...At the volt gauge on the dash, I did not put a volt meter to the compressor as yet. When functioning, the low is 35psi +/- and the high is 175-190."
Im guessing its substantially warmer than 80deg outside where you are and if it is then your pressures should be subtantially higher. The pressures should be checked with your system manually running on high fan (max cooling) both front and rear a/c and allow 10 minutes to stabilize. It appears your system charge is low. I would expect a min of 40-45psi if not higher on the low side and 200psi+ on the high side. Attached is a temp vs pressure chart. Your symptoms are standard for a system that is undercharged. The question is did it get undercharged or was it properly charged and still has a leak.

Not too mention a frosted over dryer/accumulator is a tattletale for a undercharged system. Your evaporator is icing over also because the refrigerant pressure is not above 32deg. Your humidity in the vehicle is freezing instead of evaporating at the evaparator which is what happens on a undercharged system (home a/c, refrigerator/freezer, window unit and even auto a/c).

Thanks for the detailed response, Rock.
I will get the gauges on them later today or tomorrow as you outline above and report back.
It's actually been pretty nice on the CT shoreline - 80-85 degrees most days.

 

[rockola1971]

Thanks for the detailed response, Rock.
I will get the gauges on them later today or tomorrow as you outline above and report back.
It's actually been pretty nice on the CT shoreline - 80-85 degrees most days.

"45 mins into an hour drive, the airflow through the vents slowed down drastically."
The airflow dropped drastically because your evaporator was a solid block of ice which means the refrigerant in it was below 32deg (low pressure...aka undercharged). This would not be possible if your compressor clutch wasnt working.
80-85 deg ambient temp should result in 40-55psi on the low side. As the ambient temp climbs so will your min low and high side pressures. Thats just the nature of the beast. All a/c type systems are at the mercy of the ambient temperatures their condenser and evaporator coils are subjected to. Especially the condenser coil.

So you need to know what the outside ambient temp is to get a clearer idea of what your min pressures should be when operating normally.

 

[Sambrutay]

I am turning to the experts here because I'm banging my head against the wall with the ac system in the truck.
Some backstory:
Had an ac leak at the rear evaporator (no surprise with the age of the truck).
Replaced the rear lines and evaporator = leak gone.
Had the system recharged to spec'd pressures - still no leak.
Replaced the high pressure sensor, ac compressor relay, ambient temp sensor and the evap temp sensor.
Intermittent cooling persisted so I pulled the relay and jumped it. Compressor comes on and stays on so I replaced the relay.
AC runs cold for 15 mins or so after start up and then goes warm. Occasionally, it will come back on but it didn't seem to have method to its madness.
Until I noticed that when the volts drop off to 12~ at highway speeds, that is when the ac compressor kicks off and the air goes to ambient temp from the vents.

My troubleshooting mind points me to the compressor clutch but I really wanted to see what you all thought...

Thanks in advance.

I am battling this same problem. Once the voltage drops the ac clutch falls out. I have been turning the lights on which tells the system to maintain 14+ volts and that works, but I really want to get to the root of the problem. Measured air gap of the ac clutch and it is just over .030 which is a bit out of spec. I also checked the ohms of the field coil and it fell into normal range but failed to remember exactly what it was. Seems like 3.9 ohms if I recall. But on thing I haven’t done is checked with the field coil being hot.