ac compressor cycle times?

[CLOISER]

my ac system has an electrical problem somewhere and not really finding it yet, so I'm thinking of just hardwiring a switch to the compressor for the time being because everything works except compressor not getting power

so I'm wondering what the cycle time for AC compressor is

I'm guessing compressor runs continuous in max cool and fan on high but want to make sure

[joe_peters]

Different strokes for different folks...

BASICS--year/engine?

Could your compressor not be cycling due to the low pressure cut off?

[CLOISER]

oh sorry, 1998 4.0

no pressure is good it is purely electrical problem, tried jumping switches but would love to jerry rig it till i got the time to sort it out

[joe_peters]

Ok, I only have the FSM up to 95, but I will look up the cycle times for that system and post tomorrow.

[tbburg]

There is no set "cycle time". You turn the AC on, and and the compressor circuit is energized. The cycle times are controlled by the high and low pressure switches.
The system pressure is based on the charge in the system(weight of refrigerant, not volume or pressure), engine RPM, outside air temp., cabin air temp, evaporator(inside) fan speed, and condenser fan speed(based on engine rpm for the engine driven fan) and the aux. elec. fan(whether it's running or not) <-- this mess is why no one can just say; " Xpsi is the pressure you need for a full charge"
When you're running the fan on high, the compressor stays on pretty much continuous, but again, it's controlled by the high and low switches, based on system pressure.

You sound like you're sure the system charge is correct. Have you connected a gauge set to it? (both high and low side?) Static system pressure(AC off) will have both high and low pressure switches engaged. They're easy to check with a continuity test(ohm reading across the terminals of the switch) If you get a reading, it's on. You can also jumper across the plug(bypass the switch) temporarily to see if bypassing one or the other switch will allow the compressor to come on. You can run with the low pressure switch bypassed.(not good for the compressor though) DO NOT run with the high limit bypassed.

"Max Cool" mode has nothing to do with the compressor. It shuts off outside air and recirculates cabin air.

hope that helps.

[Saudade]

What he^^ said! How did you check the pressures if the compressor won't engage?

[CLOISER]

saudade:
checked pressure by engaging compressor directly from the battery
tbburg: what should resistance be reading on hi and low switches? I figured max cool would have compressor running continuous, that's how i've seen it behave on other vehicles so just guessing, long term I wanna fix system, but in meantime don't wanna drive around alabama wet-back ok thanks a lot guys!

[Pelican]

I have a question somewhat on subject. I've had my '93 for six years, converted to 134a by PO with, I believe, addition only of ports. A/c has worked satisfactorily during that time with only the addition of a can of 134a approximately every 18 months. I was doing that task several days ago and realized that I could never remember the compressor cycling off. I've since tried it with controls set to max and normal and with various blower fan speeds and it did not cycle.

My first question is what kind of stress does the continuous compressor operation put on the a/c system and secondly, given this meager information, can you speculate as to which of the pressure switches (or both) would most likely cause the continuous run condition. I see how I can jumper the switches to make the compressor come on but how do I test to make it go off?

Thanks for your good advice. Tbburg's description of how this part of the system works should be required reading for anyone messing around with their a/c.

Edit: I understand that there is no difference in compressor operation between Max and Normal. It was just easier to throw that in but I realize that it may be confusing.

[CLOISER]

bump

[98NWCherokee]

Maybe try cleaning the rust or corrosion off the back of the clutch plate or try removing a shim. That solved my compressor engagement issue on my 98. Took all of about 10 minutes and my compressor engages perfectly now.

[heyhar]

Originally Posted by CLOISER

what should resistance be reading on hi and low switches?

There should be no resistance values for the switches themselves. You'll see a few tenths of resistance, but it's mostly the probes themselves. Set the meter to ohms (not M or K), and touch the two leads together. You'll see 1 to 3 tenths-that's the leads. Then, find the contact point you'd like to test. A switch basically should be all or nothing. They're either open or closed. Try searching, as a few years ago I remember a thread dealing with compressor cycling. What I've noticed through the years is that later ones cycle, where years ago, they tended not to cycle much, if at all.