AC - Weird symptoms...??

[djfell80]

To start: I did search through many posts and could not find someone experiencing this exact issue. If there is one, please let me know. Thanks in advance for all assistance!

So...just bought a 2005 Z-71 Tahoe, 215,*** miles. The AC seemed to be working mostly well when I drove it for the test drive. However, after purchase (same day) my wife, and I, went to run some errands. After shutting the engine off at one store, then starting after done shopping, the vents were not blowing cold air any longer. When straight home, no one wants to drive around without AC on a 105 degree day in central Texas.

Here is what I have found/done/etc.:
A) Compressor not kicking on. However, if you let it sit overnight it comes on at first, air cools accordingly. Then when you start to drive it the clutch kicks in and out, then the compressor stops altogether.

B) Changed the Climate Control Module (screen was cracked anyways and it bothered my wife).

C) Compressor clutch does engage when relay removed and terminals jumped.

D) Refrigerant pressures (when relay jumped) seem to be within margins for the high ambient temps (50psi/230psi+/-) however the air doesnt blow cold and the high/low lines are both warm/hot.

E) Jump low pressure switch - nothing happens.

F) I did notice dye sitting in the low pressure port (not sure if the previous owner was having other issues as well). No dye leaking from the condenser, evap, lines, fittings, etc. that I could tell.

Took it to shop yesterday and they called me to say it needed a new low and high pressure switches and the module. I said that I replaced the module, and did the tests on the switches and they only responded with "Oh...". I did also mention these items to them when I dropped it off for the diagnosis, so I am sure the service advisor did not mention it to the service technician. However, I agreed to let them keep it overnight and to get back with me, hopefully sometime today (8/2/22).

 

[S33k3r]

Sounds like your compressor is dying. :-(

 

[djfell80]

Curious...why would the pressures be close to accurate if this may be the cause? Thanks!

 

[djfell80]

Update: shop said they wanted to change high and low switches for $400. I laughed and said no thanks. Brought truck home. Put my gauges back on it, sprayed the condenser with water while running the AC on high (had thought about making sure wasn’t shutting down to too hot a condenser. It was nearly 101 outside today). Compressor stayed on and started cooling like it should. Cleaned off condenser coils.

Now idling it stays cool, but now it blows coolish on the highway and cools more when slowing down. Going to continue to try different things. Will double check charge tomorrow.

 

[OR VietVet]

I believe the key here is the sign of dye. I believe it could be overcharged. Previous owner may have just used a quick tap can from parts store. Take it to a trusted shop. Evacuate and pull a vacuum and make sure is left on vacuum for an hour to get as much moisture as can out of system and then charge to correct amount for front and rear system. Still could have an intermittent blend door problem but need basics first and that is making sure has correct charge amount and maybe even change switches while system is empty.

 

[djfell80]

I believe the key here is the sign of dye. I believe it could be overcharged. Previous owner may have just used a quick tap can from parts store. Take it to a trusted shop. Evacuate and pull a vacuum and make sure is left on vacuum for an hour to get as much moisture as can out of system and then charge to correct amount for front and rear system. Still could have an intermittent blend door problem but need basics first and that is making sure has correct charge amount and maybe even change switches while system is empty.

Thank you for the reply. Still searching for issues. Will be recovering refrigerant myself and pulling vac. I was thinking maybe a mixture of the dye possibly clogging the orifice tube in-turn increasing high side psi causing compressor to disengage. Will be replacing high side switch when it arrives, along with the ambient sensor (just to make sure). I miss the days of simple AC design...

 

[OR VietVet]

More Information for GM GENUINE 155378

More Information for GM GENUINE 19418346

There are two designs/sizes of orifice for these rigs and I would replace yours when evacuated.

By the way, I hope you like your 05 Z71 as much as I do. I have a build thread if you start replacing items.

 

[djfell80]

More Information for GM GENUINE 155378

More Information for GM GENUINE 19418346

There are two designs/sizes of orifice for these rigs and I would replace yours when evacuated.

By the way, I hope you like your 05 Z71 as much as I do. I have a build thread if you start replacing items.

Thank you. My wife has wanted one for a long time, and when we finally brought it home, started having this issue. She hasnt wanted to drive it since, so trying to fix it so I can have my truck back

 

[swathdiver]

If yours were mine, I would empty it out, evacuate it and start over. My old Montana was still sealed but the compressor is plumb wore out. Yours going cold and hot at differing times to me has always been a low refrigerant issue.

 

[OR VietVet]

I suspected a low charge as well, when story was first told but the pressures did not indicate that. But, like @swathdiver said, start from ground zero and know what is good and bad as you go.

 

[djfell80]

10-4! I appreciate everyone's thoughts and will report back once I screw it all up more!

 

[OR VietVet]

10-4! I appreciate everyone's thoughts and will report back once I screw it all up more!

Perfect, nothing better than making things worse to make that cold beer at end of day taste soooooooo gooooood!

 

[2006Tahoe2WD]

How many miles are on the compressor? Maybe time to change it while you are opening up the system to pull vacuum/etc. I don't think they are expensive ~$225. Remember to put the correct oil back in.

 

[OR VietVet]

How many miles are on the compressor? Maybe time to change it while you are opening up the system to pull vacuum/etc. I don't think they are expensive ~$225. Remember to put the correct oil back in.

And the correct amount in the system. A lot of compressors are shipped with the correct oil and amount but if you do this, I recommend a new orifice and always a new accumulator and blow out the system while apart. That condenser can get clogged with crud and create problems. After years of a/c work in KC, Mo. and here in Oregon, I learned that just replacing one component in a system that needs all components to work correctly, it can be a nightmare chasing something like this.

 

[2006Tahoe2WD]

And the correct amount in the system. A lot of compressors are shipped with the correct oil and amount but if you do this, I recommend a new orifice and always a new accumulator and blow out the system while apart. That condenser can get clogged with crud and create problems. After years of a/c work in KC, Mo. and here in Oregon, I learned that just replacing one component in a system that needs all components to work correctly, it can be a nightmare chasing something like this.

Agree 100%. You want to avoid black death with broken parts being kicked into the system. You may not be happy now however if that happens you will really be not happy.

 

[OR VietVet]

Agree 100%. You want to avoid black death with broken parts being kicked into the system. You may not be happy now however if that happens you will really be not happy.

Yep, systems that keep you all comfy can be finicky and expensive to fix right. You love them when they work and hate them when they don't. I ran shops and if a rig came in for a/c related problems in the winter, think compressor bearing or clutch problem when kicked on for defrost mode, I would tell them to wait till spring to repair because, God Forbid, they threw all kinds of money at that system in December and then got in an accident in January and totaled the rig, they would not get the a/c benefits they paid for in December. I would just unplug the a/c compressor or remove the belt. I got lots of repeat business that way.

 

[2006Tahoe2WD]

Yep, systems that keep you all comfy can be finicky and expensive to fix right. You love them when they work and hate them when they don't. I ran shops and if a rig came in for a/c related problems in the winter, think compressor bearing or clutch problem when kicked on for defrost mode, I would tell them to wait till spring to repair because, God Forbid, they threw all kinds of money at that system in December and then got in an accident in January and totaled the rig, they would not get the a/c benefits they paid for in December. I would just unplug the a/c compressor or remove the belt. I got lots of repeat business that way.

I don't have a climate that often requires defogging in the winter but it happens. I consider it a safety feature to be able to clear the window quickly. AC is one of those things that is super annoying when it doesn't work right. Being comfortable when driving is also a safety consideration. In other words get it fixed right and soon. You are already ahead in the car "game" by having this type/model of vehicle.

 

[rockola1971]

50/230psi and both lines warm. Sounds like possible restriction to me. I would take it apart and replace orifice tube, drier, replace both service port schrader valves and do a deep vac and hold test for an hour or so. Clean that condenser from engine side to front. Oh and probably a solvent wash on the whole system.

 

[djfell80]

Well...Evac'd, changed orifice tube (not too dirty), changed high pressure switch (was told bad by shop), pulled good vacuum and recharged. Rear AC blew cold. Found front blend actuator ended up failing as well...Put a small set of vice-grips on the blend door to hold in correct position (ordered new actuator, be here on the 11th). Went and drove it. Cooled OK at low speeds. However seemed to blow a little warmer at highway speeds 70-75mph on the toll road. Outside temp around 90-95ish.

***What RPM do you guys recommend to test PSI? Found anywhere between 1500-2500...thanks again!***

 

[rockola1971]

Well...Evac'd, changed orifice tube (not too dirty), changed high pressure switch (was told bad by shop), pulled good vacuum and recharged. Rear AC blew cold. Found front blend actuator ended up failing as well...Put a small set of vice-grips on the blend door to hold in correct position (ordered new actuator, be here on the 11th). Went and drove it. Cooled OK at low speeds. However seemed to blow a little warmer at highway speeds 70-75mph on the toll road. Outside temp around 90-95ish.

***What RPM do you guys recommend to test PSI? Found anywhere between 1500-2500...thanks again!***

I test at idle with a/c on max front and rear. You have to give it some time to settle out. The rear has a TXV not a orifice tube so be sure that rear is on and at max to get an accurate reading.