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A/C only works in "Normal"?

K

kevabar

NAXJA Forum User
Location
Bristol, PA
My observations so far (99 4.0L stock DD)... and I live in Philly area (it was over 90 and humid today.)

A/C max: works for 4 or 5 minutes at highway speeds then kicks off.

A/C normal: system stays cold for trips from 2 minutes to 1 hour 45 minutes. However, if I alter the fan speed or adjust the temp, the A/C stops working- usually... today i changed speed and temp and it still kept working.

Because it works for almost 3 hours at normal mode, I'm thinking it is not a leaky system but rather an electrical issue? thoughts?
 
It could be the system is low on gas. Have you had it charged recently or ever? If there is a low pressure detected in the system the compressor clutch will disengage. It's possible there is enough gas in the system to start cooling but not maintain it. It also might be the compressor clutch slipping or failing.
 
Basic questions: when the system "stops working", what happens. Does the air stop coming out of the dash vents, does it continue to come out but is warm, and/or does the compressor kick off?

There is no difference in basic operation of the a/c components under the hood between max and normal modes. The only difference is that the air inside the cabin is recirculated in max mode and fresh air is brought in in normal mode. Your problem may well have something to do with the vacuum supply that controls the blend door(s) that direct the flow of air or possibly with with the electrical aspects of the switches as you suspect. I guess evaporator freeze up is possible but that wouldn't be caused immediately by just altering the controls.

If you will get back with answers to the basic questions, someone will probably have some thoughts to get you started.
 
Thanks for the replies. When it is in MAX, I believe the compressor shuts off (not sure though). The temp coming from the dash vents starts to noticably get warmer after a few minutes. I will run a few more experiments and make some more observations and post back. Thanks!
 
It could also be that your system is low causing the evaporator to freeze up. While running on 'Max" the air is being recirculated and it so cold it makes the freezing worse. When running on "Normal" warm air from outside is running across the evaporator keeping it from freezing.
 
I'm going through this with my 2000 right now. 10 minutes or so of AC use and it starts to blow warm and humid air. Recharged system, no leaks found. New compressor, did not fix it. Mechanic noticed aux. fan not on when AC system switched on. That fan is supposed to be on all the time the AC is on. Theorizes that system is freezing up due to lack of coolingfrom aux. fan. Can feel the fan relay clicking but fan does not run. He can jumper the low pressure switch and get the fan to go, and can jumper the realy and get the fan to go. New switch in low pressure side did not help. Today we realized that you can wiggle the relay and the fan will intermittently start but will not stay on. Took relay/fuse block aprt and all pins/connections cleaned and reassembled but that solved nothing. System drained and recharged today as precaution and all pressures are good. The fan just refuses to operate when AC is on. They're really scratching their heads on this one. Me too.
 
Shoeman said:
I'm going through this with my 2000 right now. 10 minutes or so of AC use and it starts to blow warm and humid air. Recharged system, no leaks found. New compressor, did not fix it. Mechanic noticed aux. fan not on when AC system switched on. That fan is supposed to be on all the time the AC is on. Theorizes that system is freezing up due to lack of coolingfrom aux. fan. Can feel the fan relay clicking but fan does not run. He can jumper the low pressure switch and get the fan to go, and can jumper the realy and get the fan to go. New switch in low pressure side did not help. Today we realized that you can wiggle the relay and the fan will intermittently start but will not stay on. Took relay/fuse block aprt and all pins/connections cleaned and reassembled but that solved nothing. System drained and recharged today as precaution and all pressures are good. The fan just refuses to operate when AC is on. They're really scratching their heads on this one. Me too.
Click to expand...

I just finished the difficult job of replacing my evaporator and heater core, but in my quest to get good working a/c I did find that my a/c relay was not working all the time. Replacing it was fairly expensive but it solved that issue (I had many). You might try a bone yard relay first. And, your aux fan is supposed to turn on a few seconds before the compressor engages (every time).
 
Shoeman said:
I'm going through this with my 2000 right now. 10 minutes or so of AC use and it starts to blow warm and humid air. Recharged system, no leaks found. New compressor, did not fix it. Mechanic noticed aux. fan not on when AC system switched on. That fan is supposed to be on all the time the AC is on. Theorizes that system is freezing up due to lack of coolingfrom aux. fan. Can feel the fan relay clicking but fan does not run. He can jumper the low pressure switch and get the fan to go, and can jumper the realy and get the fan to go. New switch in low pressure side did not help. Today we realized that you can wiggle the relay and the fan will intermittently start but will not stay on. Took relay/fuse block aprt and all pins/connections cleaned and reassembled but that solved nothing. System drained and recharged today as precaution and all pressures are good. The fan just refuses to operate when AC is on. They're really scratching their heads on this one. Me too.
Click to expand...

If i'm not mistaken, it's designed that way on the 00-01 models. I was helping a friend do some AC work on his 00 last summer and was baffled when the auxiliary fan did not come on with the AC, yet still came on at the appropriate engine temperature. I did some searching around on here and others agreed that it's designed not to come on with the AC. Why it was changed for 00-01 I have no idea. Personally I think it's stupid as the point is to help pull more air through the condenser thus allowing for cooler AC.
 
No foolin'! That is wierd. I do know that the aux fan does indeed work when engine temp gets high enough.
The low pressure switch feeds into that relay. Maybe it only triggers the fan in the case of too high a pressure? But why would that be a design type?
So what does that switch actually do? It's the one that threads in a line right behind the compressor and can be replaced "dry" and not lose any refrigerant.
 
Shoeman said:
No foolin'! That is wierd. I do know that the aux fan does indeed work when engine temp gets high enough.
The low pressure switch feeds into that relay. Maybe it only triggers the fan in the case of too high a pressure? But why would that be a design type?
So what does that switch actually do? It's the one that threads in a line right behind the compressor and can be replaced "dry" and not lose any refrigerant.
Click to expand...

The one right behind the compressor is your high pressure cut off switch (for if the pressure gets too high). The one located on top of the accumulator (also known as a receiver drier) which is right in front of the firewall is your low pressure cut off switch for when the pressures get too low.

Once again if i'm not mistaken, the low pressure switch can be replaced with out losing any freon as well.

And i'm not sure why the switch in 00-01 for the fan in relation to the AC. My 99 comes on with it and all the models prior to 00 do as well.
 
I read that great link from thebrick, and we'll take a look at the clutch tomorrow. I'm still at a loss as to why the aux fan never comes on at all during AC operation. We've had the XJ hooked up to an AC service unit with pressure gauges and can watch the pressures rise and fall and the fan just never starts.
The assumption we're at now is that the condensor or evaporator (? not sure the actual term) is icing up after a bit and no longer cooling(drying) the air. Can that be related to a non-functioning aux fan?? Or is it just a bad cond/evap?? Or.....gasp... can it be a PCM malfunction?:cry:
 
bad high pressure switch might explain everything... Max setting should run it full load which would make the high side reach the toggle point sooner than the Normal setting, so that would explain the timing. Also that other link suggests that the high side switch controls the fan operation, so there is some junction there. Just guessing since I don't know how the late models are setup.
 
We replaced the high side switch today. There is a "mystery" tan wire that runs from it to who knows where at this point. We can trace the other wires right to the relay.
I'm thinking that tan wire wire goes to the PCM but can't say for sure yet.
 
Did a little more studying last night. PCM is a fancy word for fuseblock as we used to call them back in my day.
Is there any sort of blackbox or computer tied in the this system??
 
Not exactly sure what you are saying here, but PCM refers to the engine management computer. PDC refers to the underhood fuse and relay block.
 
OP here... I had to replace my coolant lines and flush my system. In the process of testing my work, I left my XJ running for a half hour. The AC worked in all different modes- max, normal, high speed, low speed, warmer AC, colder AC. I'm thinking that engine speed has effect on my AC?
 
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