Compressor perfromance

[hannahbob]

I have a 1998 Tahoe, 2 door, 5.7 liter. Owned since new and A/C always ran very cold. Year ago, it stopped getting cold, took to dealer. Refrigerant was gone and compressor was bad. They replaced compressor with aftermarket model (at my unfortunate insistence to save $; I think it's a Murray 58950). System never seemed to get near as cold as the original system; but refrigerant also got away again; dealer could not find leak. I had them drain the system and I took car home and replaced the heat exchanger (in the heater box) and the condenser (up in front of the radiator). Dealer recharged the system and it has been holding pressure (still gets cold), but still not very cold (however the day I picked it up was cold, so I was unsure at that time; Now with hot days finally here, the system is cooling but just like 6 degrees from ambient, not enough to go driving in a hot climate without suffering). My question is, should I suspect the aftermarket compressor and replace with AC delco or GM? Do the compressors vary that much in performance/output? Any thoughts/suggestions are appreciated.

[Tim]

What are the pressure readings?

[hannahbob]

Sorry, I don't have that information. I can take the rig back to the dealership, I suppose and get more information. I was hoping folks on this site could either rule out the compressor as the problem or suggest yes it could be due to differences in compressor design or performance.

[Cusser]

Dealer recharged the system and it has been holding pressure (still gets cold), but still not very cold.

Actually, you don't know if it's holding pressure or has lost refrigerant. The low and high pressures need to be read, and the amount of refrigerant pulled out and weighed to assess performance and see if refrigerant has leaked out. The pressures - when fully charged - will establish that the new compressor is pumping OK or not.

If dealer will stand by such repair (like 1-year warranty on service), take back to dealer. But I might recommend an independent AC shop.

[hannahbob]

Ok, been back to the dealer for pressure test. Readings were: static pressure 86 psi; high side running 150 psi; low side running 68 psi.

dealer is recommending evac and charge ($189) as next step. Does this mean it's low on refrigerant?

[Cusser]

Ok, been back to the dealer for pressure test. Readings were: static pressure 86 psi; high side running 150 psi; low side running 68 psi.

dealer is recommending evac and charge ($189) as next step. Does this mean it's low on refrigerant?

Whoa !!!!

Back on June 24, you wrote this:

(Dealer said) refrigerant was gone and compressor was bad. They replaced compressor with aftermarket model Dealer recharged the system and it has been holding pressure (still gets cold), but still not very cold.

This return visit to the dealer for a follow up of incomplete/incorrect repair should NOT incur additional $$$ from you, still the same repair. They need to fix at no cost, or if you paid by credit card, dispute the charge with credit card company, as you paid for a repair, not a guess. 1998 GM Tahoe/GMC AC systems are generally pretty cold (we had 1994 Suburban and currently 2005 Yukon, in Arizona desert).

[hannahbob]

I agree, it should be covered; each time I go in there, they act like they don't remember the prior work. Losing confidence in their actual knowledge of AC systems. High pressure on the low press side perhaps suggests problems with the orifice tube? Also 150 on the high side seems low compared with the specs I see from GM. Any guesses what is actually wrong?

[Cusser]

I agree, it should be covered; each time I go in there, they act like they don't remember the prior work. Losing confidence in their actual knowledge of AC systems.

Just because they are "a dealer" doesn't mean that the mechanic/mechanics who worked on yours are the sharpest knives in the drawer. I'd try to get a refund/dispute with credit card provider and find an independent AC specialty shop.

On our 2005 Yukon, GM dealer tried several times to fix intermittent sunroof closing issue; at first "diagnosis" they said bad switch (which I doubted, as I had checked that), and nailed them down that I would pay for a fix, but not for guessing, and was assured that would be the fix. After several tries and trips for same non-closing symptom, I was able finally to get a refund (no fix = no pay). That large dealership had ONE GUY who knew "something" about the sunroofs, dealer said they called Detroit for help, etc...

Also 150 on the high side seems low compared with the specs I see from GM. Any guesses what is actually wrong?

Pressures need to be read at 1500-2000 rpm. I'll relate that on both my 1994 Suburban and 2005 Yukon XL (both R134a systems from factory, dual AC front-back), my typical low side pressure was about 35psi and high side 250psi in Arizona 105F. And both cooled very well.