2nd Gen Non-Engine/Transmission A/C compressor cycle question

[rmcintosh]

I notice my a/c compressor cycles very fast (on for 10 secs off for 10). It doesnt matter if I have the heat and defrost on or a/c on.



I checked the low side pressure and it was reading 20 with the compressor on and 40 with it off. This was done in a 65* shop.

So I added a can of R134 but that didn't change my pressure or my fast cycle problem.



It doesn't seem normal for an a/c compressor to cycle this much.

Am I still to low on freon?

I know very little about a/c systems so I am in the dark with this problem.

 

[WestTN]

Fast cycling is an indication of low charge. when mine did it, it required 2 cans to refill.

 

[LRutigliano]

I agree with WestTN, sometimes one 12oz can is not enough and 20psi on the low side is too low. It should be at least 25-30psi. If you add another can, don't forget to add one 3oz can of PAG oil (med or 100 viscosity) to protect your compressor as the system oil leaks out with the refrigerant.



One other thing to note...



10 sec on/10 sec off is 3 cycles per minute. That is not abnormal during winter months even if its 65F in your shop, especially at idle with fan blower on speed 1.



On my Durango, Truck and minivan, you can hear the compressor cycle on-off at least 3x/minute at idle even during the summer if the blower is on a lower speed or if I'm in recirc.



You could try and load up the evaporator and turn the blower higher (basically increases the evap temps above freezing because more warm air is being pulled thru the evap) and see if this stops the cycling.



Also, if you are low in refrigerant, you will notice your liquid line going from the condenser (front of truck) behind the RH battery and then to the firewall become all frosted in the portion closest to the firewall. As you add more refrigerant, you can watch it thaw immediately before your eyes...



Hope this helps,