I have a 2001 F250 Superduty 4WD - 5.4 Gas.

The A/C Compressor is cycling on and off every few minutes all the time. It cycles when the control panel is set to vent or heat settings. I thought the compressor should only be turning on when the unit is set for Air or Defrost.

Does anyone have any idea what I should be looking for?

Thanks

 

When cycling, does the air only come out the defrost vents?

I had a vacuum line break on the firewall and the compressor kicked on when vent, defrost, or heat was selected but air only came out the defrost duct.

 

I think that the compressor is supposed to cycle every few minutes.

 

The A/C pump should be off in the vent (arrow at the face only) and floor (arrow at the floor only) settings. Any other setting will cycle the A/C pump.

 

So it's common for the compressor to cycle on for a few seconds, then click off every few minutes with the heater on? Now that it's cold, I noticed mine doing that. This can't be right. I can't believe it was engineered to start while driving at 4k RPMs on the freeway continuously every few minutes. That can't be good on parts. I've read why it cycles and about the compressor's gap. I would think once every 10 minutes would make it fail at half rate.

 

Cycling the A/C compressor PREVENTS it from failing. It cycles on during the defrost cycle to remove moisture, but it cycles on during other settings to "protect" the compressor and system.

The worst thing that can happen to an A/C compressor is for it to go for months without cycling on. That was the main cause for A/C failure in the 60s and 70s model cars that did not cycle the A/C compressor.

 

Yes, it is normal operation. Years ago, high head pressure would trip it off, now it's probably electronically controlled. It not only keeps the compressor from sitting idle for too long, but also saves a wee bit of fuel.

Engine driven 136,000 BTU units I used to work on (AF) would disengage the clutch periodically just to allow more even wear of the clutch and bearings.

 

The only reason the compressor cycles is to dry air. The compressor will not come on below a certain temperature (somewhere around 32-40 deg. F. I think). This is to prevent condensed water from freezing in the evaporator. Wear is not really so much of a manufacture concern, and on radial style compressors, periodic running is not nearly the issue that it was on the York and Tecumseh vertical piston compressors of the old days. Drying is the main concern as dry air makes no foggy windows. If you don't want it to run, use the eyes or floor only options, or the others only below 40 deg. F. It is pressure and core temperature controlled, so you will not be able to really alter its operation characteristics without some more advanced knowlege of the system.

 

I'll repeat this...

And add this...

The a/c cycling switch is a pressure sensor on the low pressure side of the a/c system. It is set to maintain an evaporator core pressure of approximately 30 PSI. Maintaining evaporator core refrigerant at 30 PSI will yield an evaporator core temperature of about 32 degrees. Regardless of the temperature control settings, or the incoming air temperature, or anything else for that matter, the cycling switch will attempt to maintain this pressure. Obviously, if the air coming into the evaporator core is below 32 degree's, the compressor should not cycle on.

If you think that your a/c is cycling to often, you may be right. It may be worth having the system tested by a professional to make sure the cycling switch, amount of refrigerant and other components are all correct and in proper working order.

 

^Thanks for the good info David!!

Question; has anyone around FTE done a mod to allow for a manual activation of a/c in defrost mode as well as the other modes? That way we would have control over when the a/c is on........a search didn't give me anything. Thanks.