A/C clutch won't engauge

[outracing]

Hey everyone, I have a 1999 XJ, for some reason the AC does not work. I checked the fuse and the relay under the hood, but they are both good. What could cause the AC pump to engage? It is starting to get hot here and the option of running the air conditioner would be nice. Thanks for your help.

 

[MUDWEISER_XJ]

you may be low on R-134A refrigerant. if you are somewhat mechanically inclined you can open the hood and there is a sensor that detects low pressure in the system. you can get a jump wire and unplug the sensor and jump the connector IIRC. this will turn on the A/C compressor if you are in fact low on refrigerant. do not do this for an extended time this is meant for checking to make sure the rest of the system works. you may double check this information for the 99 to make sure that you don't hurt anything. I have used this method before but it was on my GM product.

 

[souske]

Or you can unplug the single pin connector, put a paperclip in the side that goes to the clutch, and touch that to the positive terminal

 

[outracing]

So I bypassed the sensor and nothing. I checked on the other 99 xj in my drive to make sure that had the right thing and the pump instantly kicked on. I unplugged the single pin connector and touched it to the positive battery terminal and it fired right up though I'm not sure what this means. I feel like I should mention that I just bought the little xj less then a week ago. thanks for your help everyone.

 

[souske]

Your clutch works
probably something in the wiring

 

[outracing]

any ideas? Is there something that commonly fails in the wiring?

 

[Ecomike]

There is I believe a low pressure and high pressure switch, 2 switches or a 4 pin switch, my 96 Ford has a 4 pin and a 2 pin switch, either can shut down the clutch power. Also the power relay to the clutch gets its signal from the PCM and or AC blower and AC dash switch. Usually the PCM powers up the E-fan and clutch at the same time!!!!!!

There maybe a bleed diode in the power wire to the clutch coil. The clutch needs a good 12 volts and a good <1.0 ohm ground, or the clutch will not engage!!!!

 

[outracing]

I jumpered both Pressure sensors and she kicked on. I headed down to my local AutoZone and bought a can of recharge r134. It was a 20 ounce can. I followed the instructions as printed on the can and the condenser kicked on while the system was filling. I thought I had solved (maybe even temporarily) my problem. Now my issue is that the condenser doesn't disengage while the ac is in the on position. Also the air coming out of the vent is only mildly cooler then the outside air. The radiator is clean on the front and none of the fins are bent up. The low pressure side of the lines is very cold to the touch and the high pressure side is hot to the touch when the ac is running. Any ideas on what could be wrong? Thanks everyone!

 

[souske]

The clutch not cycling sound to me like its never building full pressure.
which means:
it is still low on refrigerant
or, you have a leak ( which is likely how you got here in the first place)

I supposs the swich could be bad as a third option

Hopefuly someone more ac savvy can confirm or correct this

 

[CharlesS]

The system on my 1998 only holds 19 ounces of R134a; that is a factory weighed in charge.
With the suction line cold and the discharge line hot; I would recommend you connect gauges and see what the pressures are actually at.
You might be a little over charged if you added 20 ounces.
With the vehicle stationary, the condenser fan running and the engine idling; the suction should be around 40-45 psi and the discharge should be around 300-325 psi. This pressure will drop when the engine rpms are increased or when the vehicle is driven and air is pushed thru the condenser and radiator.
Those pressures should provide you around a 45* air temperature depending upon what the outside air temperature is.

 

[Ecomike]

The condenser does not engage, it is a radiator in front of the radiator....., the clutch does. You need to get a good set of gauges and learn how to interpret pressures under different conditions, and use a temp gauge as well. Sounds like the compressor and clutch are OK, unless the shaft seal has a leak.

I jumpered both Pressure sensors and she kicked on. I headed down to my local AutoZone and bought a can of recharge r134. It was a 20 ounce can. I followed the instructions as printed on the can and the condenser kicked on while the system was filling. I thought I had solved (maybe even temporarily) my problem. Now my issue is that the condenser doesn't disengage while the ac is in the on position. Also the air coming out of the vent is only mildly cooler then the outside air. The radiator is clean on the front and none of the fins are bent up. The low pressure side of the lines is very cold to the touch and the high pressure side is hot to the touch when the ac is running. Any ideas on what could be wrong? Thanks everyone!

 

[Ecomike]

Those pressures look way to high to me, mine run around 225 and 25 psi.

The system on my 1998 only holds 19 ounces of R134a; that is a factory weighed in charge.
With the suction line cold and the discharge line hot; I would recommend you connect gauges and see what the pressures are actually at.
You might be a little over charged if you added 20 ounces.
With the vehicle stationary, the condenser fan running and the engine idling; the suction should be around 40-45 psi and the discharge should be around 300-325 psi. This pressure will drop when the engine rpms are increased or when the vehicle is driven and air is pushed thru the condenser and radiator.
Those pressures should provide you around a 45* air temperature depending upon what the outside air temperature is.

 

[Shorty]

Those pressures look way to high to me, mine run around 225 and 25 psi.

what refrigerant are you using (R134a or R12), and what ambient air temps versus duct temps are you seeing?

mine gets close to 300psi on the high side at +90* (but not quite there) and shows closer to 40psi on the low side under same conditions. The duct temps are between 38* and 44* at 40mph using the "meat thermometer" probe and about 3* colder using an IR pyrometer.

This is an R12 system (1994) that was converted to R134a before I bought it. I'd have much rather still had the R12 system since I'm swimming in R12 and only have one Jeep left that uses it :shiver:

 

[CharlesS]

Those pressures look way to high to me, mine run around 225 and 25 psi.

As I said.... those pressures and temperature are at idle... They will drop when the vehicle is driven and air is pushed thru the condenser and radiator. Probably around 30-35 suction, 250-270 and around 35* depending upon OAT.
With pressures as low as you are referring to; the OAT must be in the 70's.

 

[Ecomike]

Using R-134a on all my rigs right now.

Have not checked temps in a few years now. I replaced the condenser on my 87 with a 97, new parallel flow condenser and got the head-high side pressures about 100 PSI lower, down to about 225 at idle on a 95 F Houston day, with the AC on Max, blower on max and ......no outside air (IIRC), and it may have been a bit higher using outside humid air, but it has been a good while since I was working on all of them at once. All I clearly recall is getting from >>300 psi numbers to about 225 on the high side. For some odd reason the 89 was OK with the OEM serpentine condenser, hit maybe 235-240 psi IIRC. I usually test from start up at Max fan speed, max AC settings on recirculation (my normal settings in Houston) at idle for 20 minutes to look for possible pressure and temp peaks. Sometimes I use outside air...for the tests, but I never drive with outside air on.

I do have the E-fan hot wired in the summers and a ZJ clutch on the 87. The guys at ACKITS.com told me 300 was too high, and suggested the parallel condensers. Helped with engine peak temps as well when I swapped it out.

what refrigerant are you using (R134a or R12), and what ambient air temps versus duct temps are you seeing?

mine gets close to 300psi on the high side at +90* (but not quite there) and shows closer to 40psi on the low side under same conditions. The duct temps are between 38* and 44* at 40mph using the "meat thermometer" probe and about 3* colder using an IR pyrometer.

This is an R12 system (1994) that was converted to R134a before I bought it. I'd have much rather still had the R12 system since I'm swimming in R12 and only have one Jeep left that uses it :shiver:

 

[Ecomike]

My memory may be foggy on the 25 low side, may have been 35 peak.