Questioni have a 2001 silverado 1500 with a 5.3 and today the ac started to blow warm. i checked the system and it was full and at the correct pressures. when i start the truck it blows ice cold then it gets warm and compressor seems to engage and disengage during this the truck wants to die. then it goes away and blows cold again. always warm while driving
AnswerKris,
What were your pressure readings, and what was the temperature outside? When you took them was the truck at idle? It should be at roughly 1500 RPM when you check them.
First there is nothing in the A/C system itself that should make the truck want to die out. If that is happening, I recommend taking it into a reputable service shop.
But I will expand with what information I have.
Inside your system you have 2 safety switches that shut down and protect your compressor. The first is a low pressure switch that disengages the compressor when the pressure gets too low. Low pressure could be caused by many things, the most often of which is a low refrigerant charge. That would be my first bet. As you are driving down the road, the compressor is turning faster, therefore it is pulling a lower pressure on your low side. You said it was at the correct pressures, and I don't know your level of knowledge on A/C systems, so I will take your word for it.
If the charge is correct the another source of low pressure would be a restriction in the refrigerant line somewhere. Usually occurs at the orifice tube (metering device) entering the evaporator. There is a small screen at the inlet of the orifice tube that is there to protect any particualtes from making it past. But this is a rather in depth replacement, so I would check and verify the pressures again.
The other switch is your high pressure switch that disengages the compressor during high pressure incidents. High pressure is usually caused by the condensor, in front of your radiator, getting filthy blocking air flow through it. Take a regular garden hose and clean it out, even if it is not restricting airflow, this sure won't hurt.
To check if your low pressure switch is what is causing your compressor to shut out is easy enough. First locate the switch, it is typically located on your accumulator (an aluminum container about the girth of a soda can with two lines running out the top of it) Disconnect this switch and with an insulated wire jump the connections inside the harness. Raise your engine RPMS to about 2200-2500 and leave it there for a minute or two. If it stays running, hook the connector back to the switch, raise the RPMs again, and watch the compressor. If it cycles on and off then it is a low pressure situation. 9 out of 10 times due to a low charge. But I have to say, DO NOT, DO NOT, DO NOT leave the switch bypassed for normal use. This will cause all types of expensive problems.
I hope I helped you out a little. If you can send me the pressures and temperature, I may be able to help more. Thanks for the question.
