I have a 1994 cherokee, The A/C compressure shorts cycles like its low on refrigerant. I hooked up the guage on the low pressure line and it jumps up and down everytime the a/c pump cycles. It reads 35psi for 2 seconds then 100 to 125 for 5 to 6 seconds. The low pressure line gets very cold very fast. No cold air comes out the vents inside the car. I don't know enough to know whats going on with this thing.
Any insight would be great.
You are probably cycling off the high pressure cut-out switch-you really need high side pressure readings from a real gage set...is your clutch fan spinning- moving any air???does it quit cycling when you spray water from a garden hose on it???
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......
Hi, The clutch fan works ok. Seems weird to me that the low pressure gets cold when I crank the A/C to full,I thought it was suppost to. It makes me think it has enough refrigerant and that the pump is it pumping the refrigerant it to a point. One other thing I forgot to mention was that when I shut off the car when the A/C is on it makes a hissing sound for about 8 seconds, I can't tell where its comming from. At first I thought it was refrigerant, But it does it time after time and only for those few seconds. I thought it might have been some sort of pressure release.
Thanks for any advice.
This is a TXV system. They do not cycle based on the low side pressure like a CCOT does. In normal operation, the compressor should only cycle off based on evaporator temperature. This occurs slowly and only after the vents get cold. At idle under max cooling conditions, the compressor should run continuously or nearly so.
You really need to measure the high side pressure to know what is going on. Most auto parts stores sell professional type manifold gauges. They may be kept behind the counter and you have to ask for them.
I agree with the other posters you need to get correct pressure readings. Also be nice to know the correct refrigerant level if possible. Mastercool makes a great DIY gauge set.
Mastercool 66773 R12/R134a gauge set
Hi Guys, I'm on my way today to pickup a good set of gauges. After I take both readings I'll get back to you.
Thanks again, Jerry.
The low pressure is 10psi with clutch spinning and 35psi without.
The high pressure is 75psi with clutch spinning and 100psi without it spinning. Like I mentioned it does this every few seconds and the one line gets cool pretty fast.
Looks like a leak in the system somewhere.
How do you spell "evaporator"? Do you have a sniffer?
Hi, Dougflas I'm not to bright, Are you saying theres a leak in the evaporator. I don't have a sniffer. Sorry for the ignorance.
Chrysler are known for evap leaks but that is just one of many areas to check.
Humm, Just to be safe maybe I should replace the usaual supects, Being that it is a 94.
Thanks guys for the help.
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