Another A/C Thread......I Know!

[Danell Fullbright]

Ok, I know yet another a/c thread.

I have a 2003 Chevy Tahoe 4.8l. The a/c will blow cold upon startup and may run fine the entire time I'm driving. Other times, it will still start cold, and then turn to blow hot. Blows hot on both driver and passenger side as well as the rear air.

I have already replaced the blend door actuator as well as the HVAC control module without any change.

Any suggestions on where to go next?

 

[OR VietVet]

Welcome to the forum from Oregon.

The first thing that should have been done, before replacing those parts, was to put gauges on the system and monitor it for pressures. You could just be low on refrigerant. You could have a failing fan clutch. You may have a partial blockage at the air flow across the condenser. You may have a compressor problem or a pressure switch problem. If that a/c compressor clutch is disengaging, besides cycling, it could be a simple clutch cycling switch.

 

[JonnyTahoe]

Welcome to the forum from Oregon.

The first thing that should have been done, before replacing those parts, was to put gauges on the system and monitor it for pressures. You could just be low on refrigerant. You could have a failing fan clutch. You may have a partial blockage at the air flow across the condenser. You may have a compressor problem or a pressure switch problem. If that a/c compressor clutch is disengaging, besides cycling, it could be a simple clutch cycling switch.

New Pressure Switch still cycling. 20 oz can of A/C PRO with the pressure gauge on the can still warm air. Compressor bad possibly?

 

[OR VietVet]

What are the pressure readings when not cycling and when is cycling?

 

[JonnyTahoe]

What are the pressure readings when not cycling and when is cycling?

The Can of A/C PRO Gauge goes down to 25-30 while the compressor is engaged. 60 when not engaged. These are Low line pressure readings. I did the recharge yesterday and the outside temp was about 90 with low humidity. We are experiencing July heat in early June that will last another week. The small 'self-sealing' cans of 134a Do Not work! A/C PRO is the only brand of refrigerant I could get to work. The compressor only engages for 5-8 seconds then shuts off for about 20-25 seconds. I replaced the Pressure Switch with a new one Saturday.

 

[OR VietVet]

That scenario you just described tells me the system is low and/or your compressor is taking a crap if you cannot get it to pull the refrigerant in.

 

[JonnyTahoe]

That scenario you just described tells me the system is low and/or your compressor is taking a crap if you cannot get it to pull the refrigerant in.

That's what I am thinking. This Yukon is a life long Texas truck think of the years of using the A/C. If it's the original compressor that's a pretty good run. Truck has 171K on it. Worked great last year. The one time we have once in ten year heat my A/C stops working.

 

[OR VietVet]

If you do change out the compressor, make sure you give the a/c system it's best chance for a long life after that. Replace the accumulator, access evaporator thru the blower motor if can and clean it off, replace the orifice, completely clean and blow out both sides of the condenser and flush the system out while all apart. If you just do a compressor, I believe you will regret it soo, but again, I could be wrong.