2nd Gen Non-Engine/Transmission A/C cycle time during defrost

[Ncostello]

I understand the A/C compressor will run when the defrost is on... even when on hot temp. But my trucks compressor will run for 7 seconds, stay off for 10 seconds, run for 7 seconds... etc. It does this the whole time the defrost is on.



In true A/C conditions it will not operate like this. I believe the compressor runs for longer periods when the A/C is actually selected. Is this a normal cycle during defrost?

 

[B.G. Smith]

The AC cycling is controlled by the clutch cycling switch which senses suction pressure to the compressor. It is screwed into the side of the accumulator. The suction pressure/cycle time is dependant on heat load of the system, you probably don't have as much air passing over the evaporator in defrost mode as you would in ac so the heat load would be lower, cycle time shorter. Of course the switch could be going bad or you might be a little low on refrigerant. The switch opens at about 25psi and closes at about 43psi. bg

 

[wtrenholm]

As BG Smith said it's related to heat load. Basically we want the surface temp of the evaporator to stay just above freezing. That way we get the best heat absorbsion into the evap/refrigerant but will not freeze the condensation on the fins of the evap. We hear that complaint when the cycling switch fails to turn the compressor off.



So as temp or humidity lowers, your cycling times will change. Shorter "on" time and longer "off" time.



HTH

Wayne