Automotive Air Conditioning Information Forum (Archives)

emigudnuf on Thu July 15, 2010 2:26 PM

Year: 1999
Make: jeep
Model: grandcherokee
Engine Size: 4.0
Refrigerant Type: r134
Ambient Temp: 95
Pressure Low: 38
Pressure High: 37
Country of Origin: United States

hey all. my daughters jeep grand cherokee 1999 4.0 had great a/c. she was driving and in one day went from cold to hot air.( i found out 2wks after kids huh.) any way i checked pressures with my guages. static was 38 low side and 37 high side. its almost 95 here today . started it up and let run 10 min and pressure stayed the same. clutch not cycling on and off at all.. shut it off and let it cool down and started checking things. at the compressor the 2 wires going into the compressor switch were melted together from touching the exhaust manifold. i made the repair thinking that this was it. put things back together ( stupid me i never checked to make sure 12v was running to it after repair) anyway started it up and the same thing. no cool air and no cycling. daughter had to leave for some bs thing with her boyfriend so i didnt get to check anything else again. could just the switch on the compressor have burned up when wires melted? any ideas guys about this? thanks

jglanham on Thu July 15, 2010 3:11 PM

Unlikely the switch burned up. Check for blown fuse(s).

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johnl

mk378 on Thu July 15, 2010 3:23 PM

Static pressure 38 means there's been an almost total leak out. Need to find and fix leak evacuate and recharge. If it's a TXV system the pressure switch usually needs about 50 psi before the compressor will start.

Edited: Thu July 15, 2010 at 3:26 PM by mk378

emigudnuf on Thu July 15, 2010 5:33 PM

thanks guys. but what is a txv system? and how do i tell if she has that? any idea what could of caused the system to leak out so quick ? or maybe when the compressor wires burnt the compressor took a dump and blew seals or something?a/c was working great then bam. all happened in one day. thanks.

HVargas on Thu July 15, 2010 7:27 PM

TXV just means the system has an expansion valve instead of an orifice tube. Your system has a fixed orifice tube. First thing is to get it evacuated and recharged with dye so you can leak check it. With 38psi, the compressor will not kick on. That is nearly an empty system. At 90*, you should have well over 100psi of static pressure.

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emigudnuf on Fri July 30, 2010 11:03 AM

hey all finally got to re-look at daughters jeep. checked for power going to the compressor and i got nothing . i checked fuses under dash and under hood and all fuses are ok. i then ran 12v directly fromthe battery to the compressor and it kicked on. un hook wires and it kicks off. hooked guages up and i still have the same static readings. tried to put r134a in and it wouldnt take any cuz the compressor not cycling. jumped the wires to the compressor and it kicked in but seemed like it still didnt want to take any. the ac switch in the dash turns green ( for on) when u push it. why am i not getting power to compressor? should it have 12v at all time or does something kick in ( like a pressure switch or something) allowing the power to go to compressor? thanks all

mk378 on Fri July 30, 2010 11:54 AM

Pressure in a can of refrigerant is about 100 psi, more than 35 psi, so it will go in with the engine off. Get a can with UV dye included, hold the can upside down and charge it into the HIGH SIDE with the ENGINE OFF. This should raise the pressure enough to close the switch (mounted on the accumulator). If the compressor still doesn't run, need to find the electrical problem. Melted wires would almost certainly blow a fuse somewhere, the question is where. I don't think Jeep has the GM type compressor lockout software, but you could try resetting the computers anyway by disconnecting the battery.

Use one can with dye the rest plain R-134a. You only need to put dye in once. Also avoid running the compressor with a low charge, certainly don't jump it with the system empty.

HVargas on Fri July 30, 2010 1:22 PM

As already stated, you need to have way more than 38psi static pressure to kick on the compressor. You should have 12v into the pressure switch, but it will not release the 12v to the compressor without a certain pressure reading. Evacuate what is in the system, find the leaks, fix and vacuum and recharge with the specified amount of R134a.

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