ntheath

Hello all,

I found this forum board while searching the net for help with my Tahoe AC problem. In a nutshell, my compressor failed last last summer and I limped along until it was cool enough to not need AC here in NC. At the time, I noticed that it was failing because of the nasty noises it was making when I would turn on the AC (sounded like a huge stick in my fan whenever I would accelerate after turning on the system). The AC system still blew cold air in the front, but the rear was hit or miss after the compressor started making nasty noises.

Fast forward to now, I recently had a shop discharge the system, I replaced the accumulator, orifice tube, and the compressor, and then had the shop recharge and test the system. When I picked it up the front and rear blew cold as ice. Today I noticed though, that the front is cold but the rear is back to being warm (because its not hot here yet). Can anyone guide me to what might be going on here ? I don't have rear heat, just speed settings on the rear ac panel. Also, the rear blower is fine - it blows air no problem. I am wondering what might have failed in the original compressor which might have damaged the rear portion of the AC system. The old compressor had no oil in it when I pulled it which explained the nasty noises so it was definitely dead.

Any tips are much appreciated!!!

thanks,
nick

73shark

Welcome to the forum.

I'm wondering if the failing compressor let go of some pieces and they carried thru the system and clogged the rear system.

ntheath

Sounds reasonable to me. I don't know where to start though, I need to get a diagram of the rear system so I can figure out where the most likely places are to clog.

nick

ntheath

So on the way home yesterday, the rear AC was working. Seems like it is hit or miss. This was the same behavior before I replaced the broken compressor. I am wondering if there is a valve or something in the back which is not opening all the time?

in2pro

I would suspect a blend door is sticking, as your rear ac also provides heat in the winter.....

ntheath

I'm not sure mine provides heat - as its never before when I tried. The control for the rear AC only says AC and it only has one **** for fan speed. My understanding is that meant it only provides AC and not heat? If that's not the case, then I totally agree and hope that's all that's wrong. My worry is that when the compressor went out initially, it did damage something in the back inside the pressurized system. I still need to inspect the temperature of the lines running back there. What's weird is that its intermittent, I wouldn't expect something in the lines to cause it to be that way?

thanks,
nick

in2pro

Check under the vehicles rear quarter panel where the rear cooling unit is located, if you see 4 lines/hoses it has the heating and cooling, if you see only 2 lines then its probably only cooling....

give the attached a read and see if it helps identify any possible issues...

ntheath

Thanks, I'll take a look at the document. I did check the car during lunch, it only has two lines so looks like AC only. Is there a separate blending mechanism in the back?

nick

RacerX

no. in the rear there is another evaporator. It is before the tires on the left or right but plumbed up from the floor. The thing could be a bad evaporator(do you smell anything in the car-like wet dirt) or simply worn O-rings. The system holds a capacity of 3lbs freon(front and rear controls).

Bad compressors dont discharge into the system. They just seize up. And usually from low oil level internally.

I would guess the rear evaporator is bad. But you will have to do a leak detection test to check for sure. No doubt the shop you went put the dye in the system, you just have to crawl under the car and check.

ntheath

Ok, well its a relief to know that the compressor wouldn't screw the system up like that. The old compressor was indeed out of oil, when I went to drain and measure nothing came out! It hadn't seized yet, but was on its way if I had continued to use it. The shop did use the dye as they charged me for two cans. They put in 3 lbs of R134a - the original (cleaned by their machine) 2.3 lbs pulled from the system on discharge and 0.7 of a new can. My tahoe has 129k on it so I assume the R134A was low from normal leaking over time. Plus, the high and low side valves were leaking once they filled it back up so they had to replace those. Maybe the rear has been leaking for a little while and I didn't really notice it until the compressor started to die?

This morning I tried the rear AC and it appeared to work fine. Seems like this issue is picky, would a bad evaporator exhibit this behavior or would it just be bad all the time?

As far as the leak detection, what I am looking for? Do I need a black light to see the dye?