2003 GMC yukon XL / Chevy Suburban

[jdv]

Good Morning.

I have a new to me 2003 GMC yukon XL. I bought it knowing that the front AC was blowing what seemed to be ambient air(I test drove it in Pacifica, CA which is on the coast), so it felt slightly cool but I knew that the system for the front was not working properly. The rear system was blowing cold air. The owner suggested that it would be as easy as recharging it with AC in a can, but I wanted to rent the proper gauges and take a better look at what I am dealing with. Here are my findings. Thank you in advance for your feedback.

Ambient temp. 65 degrees
Humidity 80%

Low side High side
vehicle not running 76# 80#

Start up @idle AC off 78 80

Front AC only @ idle 48# Comp. turns on drops to 23# 80# Comp. turns on rises to 100#

Front and Rear @ idle Comp. on and stays on. 30# 130

Front only again @ idle 48# Comp. turns on drops to 23# 87# Comp. turns on rises to 107#

Front only @ 1500 rpm 44# Comp. turns on drops to 20# 80# Comp. turns on rises to 100#

Front only @ 2000 rpm 44# Comp. turns on drops to 16# 80# Comp. turns on rises to 100#

Front and Rear @ 1500 52# Comp. turns on drops to 24# 105# Comp. turns on rises to 135#

Front and Rear @ 2000 54# Comp. turns on drops to 23# 100# Comp. turns on rises to 130#

Shut down Gauges equalized @ 50# for both Low and High

[tbirdtbird]

You have a leak.
I would obtain an electronic sniffer and go over the entire system to check for leaks while there is still refrigerant in there.
Please do not be tempted to just install a can or two of 134.
And whatever you do, do NOT install one of the "death kits" from the auto parts store, ie a fancy looking can of 134 with additives and sealers that promise to fix everything. This stuff will clog your system horribly and destroy it.

Be patient and wait for the next consultant to weigh in before you make any decisions.

[JohnHere]

An ambient temperature of ~65°F is somewhat mild for testing system performance. Around 80°F or higher would be better. Regardless, based on your pressure readings, I agree that the system seems to have a leak someplace even though it's the rear A/C that blows cold.

Do you happen to know whether the vehicle spent all its life in California or somewhere in the so-called Rust Belt at some point? The reason I ask is because over time, Rust Belt vehicles can develop pinhole leaks in the metal refrigerant lines mounted down low due to corrosion. Even California vehicles can develop similar leaks if exposed to years of salt air.

[jdv]

This vehicle spent its whole life garaged in California.

Do any of the measurements I took suggest anything else with maybe a specific part of the system? I will see if I can identify any leaks this evening.

[JohnHere]

The place to start would be to leak-check the system, as you suggest, while the system is still pressurized. Look for oily spots and/or traces of green fluorescent dye on all visible A/C components and connections. Also look for dye in the condensate that drains from the evaporators (under the vehicle). If no leaks can be found, the problem might be due to very slight seasonal losses at the compressor shaft seal, especially if this 19-year-old vehicle never had its A/C system serviced.

Next, recover the existing charge, or have it done, to determine how much refrigerant is in it now, and then recharge it to the correct amount by weight.

The specification that I have for your vehicle is 48 ounces of R-134a.

[jdv]

Looked the system over and didn't see anything obvious until I took the cap off the low side charging port. There was pressure behind the cap and sounds of a leak. Sprayed some soapy water at it and it looks like it is leaking from the Schrader valve. I will have to replace the valve, but should I replace anything else while I have the system discharged? Or if it's not broke, don't fix it?

[tbirdtbird]

Don't let that fool you. The schraders will often leak a small amount. The final seal, believe it or not, is the cap that goes on there, it should have a rubber gasket inside. If you have the proper schrader tool, you could try snugging up the schrader core a bit but do not over tighten. BUT you still need the plastic cap
You will have a lot of trouble trying to fix this until you get an electronic sniffer as mentioned.

EDIT: Wait, you already discharged the system before the final leak sniffing?
Evaps and hard lines under the vehicle as JohnHere mentioned are the usual culprits.
To check the compressor seal, remove the drive belt and put a shower cap or plastic bag over the comp and pulley, and next morning stick the sniffer wand inside to see if you get a hit

[DetroitAC]

With a truck that old, you might not have a leak that can be found, might just have normal leakage. All AC systems leak with time, this is normal.

You are just low on refrigerant. Have the existing refrigerant recovered, have it charged to the weight listed on your under hood sticker.

[Cusser]

With a truck that old, you might not have a leak that can be found, might just have normal leakage. All AC systems leak with time, this is normal.

You are just low on refrigerant. Have the existing refrigerant recovered, have it charged to the weight listed on your under hood sticker.

My 1994 and 2005 Suburbans (R134a) had UV dye added at the factory, was an underhood sticker. The 2005 Yukon XL/Suburban never had a refrigerant leak while we owned it (2010-2021) but I did install a new compressor due to "slugging"/breaking belts. I agree with what was posted above, and have it leak checked a few days or a week later, looking for UV dye, even in the two evaporator condensate drains.

The shop that evacuates and measures the amount of existing R134a should install two new schraeder valves. And install a brand-new cap. Last summer I fixed a slow R-12 leak on my 1988 Mazda truck with a new cap (new low-side schraeder not installed because system was not empty) and this summer similar on low-side on my 1998 Frontier with R134a. I'll install new schaedrer valves next time the systems are empty: inexpensive and they do go bad/get worse.

[jdv]

I am waiting for my new gauge set and sniffer to show up. I am thinking I will top of the system with some of the dyed r134A and see if I can get the system up and operating again. Then I will look for leaks again, to see I there is anything other than the low side schrader valve leaking. Thanks for the input and I will get back with what I find.