'99 A/C question?

[Ozzie]

Hey All,

I have a 1999 Tahoe 4x4 with 137,000 miles. I had the A/C unit recharged last summer (2011) for the first time. Worked great. This last week it got hot enough to turn it on again. I engaged the A/C button and it did not get cool at all. When I was parked, I tried it again. I can hear the compressor turn on and then in about 8 -10 seconds it cycles off. Then it comes on again and cycles off. Is there a component that either senses that there is not sufficient coolant pressure and shuts it off or is this another component or the compressor itself?
Any ideas or suggestions would be most appreciated!

Thanks,
Ozzie

 

[lesterl]

There are pressure sensors, you likely are low on freon tho.....

 

[Ozzie]

OK... next step?

I got the kit and went thru the process of recharging. Pressure came up nice and stayed in the green as ling as I kept adding coolant. As soon as the canister was empty, the pressure dropped back down. So, I assume a leak somewhere is the culprit. Time for an expert or should I try something else?

Ozzie

 

[lesterl]

What was the pressure before you added? IF it were 0, then you probably have a big leak, did you hear it hissing out?

When you charged it, did you have the engine running, the AC on HIGH? What pressure did you attain, what did it drop too when you stopped? Did the Compressor ever kick in?

 

[Ozzie]

Engine running & AC on high. Initial pressure around 10psi. Compressor kicked in after adding coolant for about 15 seconds and stayed on. Attained about midway thru the green zone and it stayed there until canister was empty. Pressure then dropped back down close to 0-10 psi. Only hissed when I removed the low pressure cap, briefly.

 

[lesterl]

May still need refrigerant, my system took 3 cans of freon.

If your system hissed when you actually removed the dust cap, you need valve cores, lemme look up the part number for ya.....

 

[Ozzie]

Wow. 3 cans. This was the 22oz. bottle. I am a total novice, so if I need the valve cores, are they difficult to replace? I'm willing to give it a try. I should be able to check the low side pressure again with the same gauge on the empty bottle, should I not? Are the advertised sealants worth using?
Thanks,
Ozzie

 

[lesterl]

MT2901 from autozone is one of the kits I have purchased before, one had a valve core tool....

Cores unscrew like a screw, screw back in same. 20 second fix (will loose freon tho).

 

[Mrslyfox]

do you have front and rear air or just front? I believe the front and rear air systems take 36oz of freon plus oil. Also if you were down to zero you need to do a system vacuum, replace the orifice tube and maybe the drier. Non of which are terribly expensive, but the only way you will get it to work properly. If you heard a hissing sound you have a leak somewhere. Get a can of dye, or freon with dye in it, you will easily see where it is leaking from. It is common for these to get a leak under the right side frame for the rear air, and that can be expensive to fix. I bought a kit to shut off the rear air lines instead of replacing. Its mostly just me in my vehicle and I dont notice any difference with the rear air off. I just refilled mine, still seems to be a extremely minor leak, probably from the kit I installed, an o-ring I imagine, have to fill it maybe 2 times through the summer, but cheaper than doing a major overhaul at the mechanics. Anyway, my thought is you have a leak somewhere and putting more freon in at this time is a waste of money. If it is just the valve core(s), simple fix, no special tools needed, like the above post, unscrew and screw new one in. If you are going to be doing all this yourself, it would be best to invest in a good set of gauges, and a vacuum pump. When you vac it, you boil out any moisture left in the lines, and it will also tell you if you can hold pressure or not with the gauges, if you arent holding a vacuum, dont waste any money putting freon in it.

 

[hshark]

If you do not have enough freon your compressor will not engage. I do not reccomend recharging your system with any auto parts recharge kits. If you are low on freon it is because you have a leak somewhere. Take it to a shop or check your own system for leaks. Our cars tend to leak at the compressor. If this is the case you need to have it repaired. If you want to check for leaks yourself get a sprayer with soapy water and turn the key on. just the ignition on not the engine. Turn your a/c on and begin spraying the solution at the compressor. If you get any buble formation you have a leak. If no bubles at the compressor move onto hoses etc. I believe our system takes about 1kg to fill.

 

[Mrslyfox]

If you do not have enough freon your compressor will not engage. I do not reccomend recharging your system with any auto parts recharge kits. If you are low on freon it is because you have a leak somewhere. Take it to a shop or check your own system for leaks. Our cars tend to leak at the compressor. If this is the case you need to have it repaired. If you want to check for leaks yourself get a sprayer with soapy water and turn the key on. just the ignition on not the engine. Turn your a/c on and begin spraying the solution at the compressor. If you get any buble formation you have a leak. If no bubles at the compressor move onto hoses etc. I believe our system takes about 1kg to fill.

This is true, our compressors are KNOWN for leaking. I believe they crack somewhere. Its been a couple years since I dealt with all this but that definitely rings a bell. If you need a new compressor, you can get on ebay and find some pretty good deals, much cheaper than GM or the auto parts store for the exact same thing. Dont go with the cheapest though. Get a good one. Delphi I believe is the brand you want. You can get ones a lot cheaper, but this is one of those things where you probably get what you pay for. I do know the lines under the vehicle are prone to leaks as well from rocks and road debris being kicked up an hitting them. If you replace lines under there, I would recommend giving them a good coating of rust protectant. Have been told that is a smart thing to do. Although mine had it and they still sprung a leak. and true that the recharge kits... the cans with the gauge, not highly recommended, thats why I said buy yourself a good set of a/c gauges and a vac pump if you plan on doing this yourself. Read up and know what you are doing. If you are only doing it once, its not worth the price of a good set of gauges and pump, but buy them once, and you will always have them.

 

[lesterl]

(my 3 cans were 12oz... ----36oz). The compressor shaft seal is what goes from what I am told, it is sold separate also....

Good luck.