A/C compressor runs constantly

[metalmoto]

On many other cars I have owned. The compressor will cycle on and off, depending on the outside temperature. Like I'm used to it running constantly for the first 15-20 minutes, and then it usually starts to cycle on and off. Depending in the outside temperature, and when it has reached the maximum cooling that it can provide. It seems to cycle on and off, in the defrost mode. But when running the A/C, it runs constantly! Is this normal for a 04' Jeep Liberty's A/C system? I have hooked up a manifold gauge, and the readings seem to be very close, going by the outside temperature. The temperature coming out of the vents on a 90 degree day is about 48 degrees. This seems about right also.
Although, other cars I owned, it would get down to about 45 degrees. Also pretty close to what I have. But why does the compressor run constantly?
I read on one of the posts, that the low pressure sensor could be faulty. I replaced it, but the compressor still runs constantly. Any ideas? Thanks in advance!

 

[teeje]

On many other cars I have owned. The compressor will cycle on and off, depending on the outside temperature. Like I'm used to it running constantly for the first 15-20 minutes, and then it usually starts to cycle on and off. Depending in the outside temperature, and when it has reached the maximum cooling that it can provide. It seems to cycle on and off, in the defrost mode. But when running the A/C, it runs constantly! Is this normal for a 04' Jeep Liberty's A/C system? I have hooked up a manifold gauge, and the readings seem to be very close, going by the outside temperature. The temperature coming out of the vents on a 90 degree day is about 48 degrees. This seems about right also.
Although, other cars I owned, it would get down to about 45 degrees. Also pretty close to what I have. But why does the compressor run constantly?
I read on one of the posts, that the low pressure sensor could be faulty. I replaced it, but the compressor still runs constantly. Any ideas? Thanks in advance!

Could have a bad high pressure sensor don't quote me on that though.

 

[metalmoto]

Yes, I was thinking that too. I was able to swap the low pressure sensor from my 02' liberty. But for the high pressure sensor my 04' uses a 3 wire sensor, and my 02' has a 2 wire sensor. So I'll just have to buy one! Although the pressures seemed just fine. Not too high. So I am baffled on this one...

 

[Billwill]

Although the KJ does not have a "Cabin Filter" there is a metal grid inside on the firewall below the Glove Box that acts as a filter. This can get clogged up with debris that you need to brush off or vacumn up....maybe the cabin is battling to breath!

Replacing the high pressure sensor may help or you may need a to charge up the system or replace a compressor or evaporator.

 

[LibertyTC]

Ya there is a link somewhere about cleaning the screen. I think you have to remove windshield wipers, remove plastic cowl and then gain access from there.
The factory service manual lists hi and low pressures and temps. Do you have the FSM?
For instance on a 90F day the center vent on recirculating mode, 1000, rpm is listed at 55F as normal for the KJ.
Ya I know it aint blistering cold compared to some vehicles.

 

[metalmoto]

Metal grid in glove box

Although the KJ does not have a "Cabin Filter" there is a metal grid inside on the firewall below the Glove Box that acts as a filter. This can get clogged up with debris that you need to brush off or vacumn up....maybe the cabin is battling to breath!

Replacing the high pressure sensor may help or you may need a to charge up the system or replace a compressor or evaporator.

Yes, I discovered mine was dirty and clogged on my old Jeep. But in my new Jeep the screen looks very clean. I swapped the low pressure sensor from my old Jeep, and this didn't make a difference. The High pressure sensor on my new Jeep uses 3 wires, and the old Jeep has a 2 wire sensor. So I can't swap that.
I will just have to buy a new High pressure sensor, and see it that works.

 

[metalmoto]

Don't have the FSM

Ya there is a link somewhere about cleaning the screen. I think you have to remove windshield wipers, remove plastic cowl and then gain access from there.
The factory service manual lists hi and low pressures and temps. Do you have the FSM?
For instance on a 90F day the center vent on recirculating mode, 1000, rpm is listed at 55F as normal for the KJ.
Ya I know it aint blistering cold compared to some vehicles.

I was getting about 48-50 degrees from the center vent in 87 degree weather.
Hooked up a manifold gauge, and the pressures looked fine. Does the compressor cycle on and off on your Jeep?

 

[Billwill]

The compressor does cycle ON/OFF in the KJs when at idle....to maintain the humidity in the cabin.

Some owners have modified the system so that this does not happen but I do not think this is a big deal.

My 2002 Export CRD has the AC cycle ON/OFF while I am driving....the AC works very well in this hot climate and I have not had to do any form of maintenance on the system in all these years....I have probably jinxed myself now!!

 

[Sassy0876]

The compressor does cycle ON/OFF in the KJs when at idle....to maintain the humidity in the cabin.

Some owners have modified the system so that this does not happen but I do not think this is a big deal.

My 2002 Export CRD has the AC cycle ON/OFF while I am driving....the AC works very well in this hot climate and I have not had to do any form of maintenance on the system in all these years....I have probably jinxed myself now!!

The compressor/ac clutch in my kj don't cycle on and off at idle. If my ac is on so is my clutch and compressor. It used to cycle on and off and then i started having issues with it. Now I don't know whether to take it in to the shop or leave it alone

 

[JeepJeepster]

If its 90F out there is a good chance that it may not be kicking on and off.

It'll kick on and off when its cooler out.

Long as your pressures are ok and the high pressures arent too high you should be fine.

 

[Martinadam]

Causes of a constantly running system

There are some Causes of a constantly running system

Dirty evaporator coil.
Frozen evaporator coil.
Clogged air filter.
Restrictive filters.
Low refrigerant charge.
Faulty thermostat.
Leaky ducts.
Dirty or blocked condenser.
Blower motor and fan issues.
Incorrectly sized unit.

 

[tjkj2002]

There are some Causes of a constantly running system

Dirty evaporator coil.
Frozen evaporator coil.
Clogged air filter.
Restrictive filters.
Low refrigerant charge.
Faulty thermostat.
Leaky ducts.
Dirty or blocked condenser.
Blower motor and fan issues.
Incorrectly sized unit.

In bold does not effect automotive AC systems at all.

Low R134A causes frozen evap core but the compressor will not run all the time,it will shut down.

Clogged evap(dirty) or condenser will only cause a system efficiency reduction and overheat the engine.Again will not cause the compressor to run all the time.

In fact most automotive AC systems in the last 15+ years will actually shutoff when the engine overheats and you go to WOT.