Air Conditioning problems

[CoreyH]

hey guys,
my wife has an 02 Jeep Liberty Limited and I do not know much about a/c systems. The air starts off cold and then gets hot, then cold, then hot.....
So I have a set of gauges and at idle the low pressure is about 40psi and the high side is about 190psi. Its decent cold, cant complain about that. Now, when driving, the low pressure will jump up to around 80psi and the high side will drop down to 90-100psi. That is when the air blows warm. It only lasts for a few seconds and then goes to low side 50psi and high side 210psi. It does this while driving on the highway. In town, if you're just cruising along it does it every few minutes instead of every couple seconds. Pull into the garage and then the pressure goes back to 40psi low side and 190psi high side and it stays that way. Someone told me the compressor is bad, but if it was bad, would it not work at all???? Stumped!!

 

[teeje]

Sounds like it may be over charged. Just my two cents. Get it evacuated and re charged. Will save you some money and let you know what's going on. If it keeps doing it you know it's the compressor


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[CoreyH]

Did that today. Had it evac'ed and vacuumed, and recharged. Pressure is right, called for 1.63lbs, I have 1.5 in it to set the low pressure side at 40psi. Did this last week too and a buddy told me it could be moisture in the system freezing at the orifice but it doesn't stay warm. A couple seconds later it gets cold again when the pressure drops back down to normal. Think it really could be the compressor? It's not making any noise or anything. When I put my stethoscope on it, its quiet.

 

[Billwill]

Is the AC clutch engaging and disengaging properly?

Serpentine belt on tight?

 

[teeje]

Did that today. Had it evac'ed and vacuumed, and recharged. Pressure is right, called for 1.63lbs, I have 1.5 in it to set the low pressure side at 40psi. Did this last week too and a buddy told me it could be moisture in the system freezing at the orifice but it doesn't stay warm. A couple seconds later it gets cold again when the pressure drops back down to normal. Think it really could be the compressor? It's not making any noise or anything. When I put my stethoscope on it, its quiet.

Could also be the evaporator/ or the (whatever part is in the dash I can't think of the name right now) is bad as well. Compressor could be bad because of a couple reasons. Think of the compressor as a small combustion chamber except the fact that it does not combust. There's little "pistons" if you will, that compress the freon and it in turns, makes it cold. From there it shoots out the suction line (line on top of compressor) to the evaporator and then to that part in the dash. If any of this is wrong correct me but I'm almost positive that's how it works. Also, you have your condenser that plays a big part as well. Like a radiator, brings air in to cool it down as feel. You could also have a bad low/high pressure switch being that it gets cold. Seems like the compressor doesn't know what to do sometimes so that's what I'm thinking


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[CoreyH]

Ok, also note that the accumulator and condenser are both new. A year old anyways. I did replace the compressor last summer but bought it from a salvage yard. Is there a way to test the switch to see if it's going bad? Can do process of elimination by ruling out the sensor if it's bad or not.

 

[CoreyH]

Again, at idle the a/c works perfect. Low pressure is right at 38psi and I pressure is actually 192. It's only when it's driving that the pressures start to swap and low pressure jumps up and high pressure drops.

 

[uss2defiant]

did you change the orifice tube when you changed the accumulator and condensor?

The low side pressure is too
high, and the high side
pressure is too low.

1. Accessory drive belt
slipping.

1. Refer to Cooling for more information. Inspect
the accessory drive belt condition and tension.
Tighten or replace the accessory drive belt, if
required.

2. Fixed orifice tube not
installed.
2. See A/C Orifice Tube in this group. Replace
the liquid line, if required.

3. Faulty compressor.
3. See A/C Compressor in this group. Replace
the compressor, if required.

 

[CoreyH]

did you change the orifice tube when you changed the accumulator and condensor?

The low side pressure is too
high, and the high side
pressure is too low.

1. Accessory drive belt
slipping.

1. Refer to Cooling for more information. Inspect
the accessory drive belt condition and tension.
Tighten or replace the accessory drive belt, if
required.

2. Fixed orifice tube not
installed.
2. See A/C Orifice Tube in this group. Replace
the liquid line, if required.

3. Faulty compressor.
3. See A/C Compressor in this group. Replace
the compressor, if required.

what should the low side and high side pressure be then? I was always told no matter what vehicle the low side should be between 35 and 40psi because that will be roughly what the air temp through the vents should be. On another forum they mentioned the pressures were where they needed to be. Just wondering why at idle everything is fine and why driving is when it gets hot, cold, hot cold, and the pressures flop for a couple seconds. If it was the compressor, wouldn't be doing that ALL the time even at idle?
No, we did not replace the orifice tube, just blew it out until I had air slowing coming out the other end of the line.
Also, no accessory belt. Its only the serpentine belt on the Libertys

 

[uss2defiant]

http://www.jeepkj.com/forum/f202/ac...4-refrig-oil-amount-performance-chart]-58537/

 

[CoreyH]

Would not having enough pag oil in the system cause it to flip flop on pressure like that when driving?

 

[CoreyH]

Reason I ask is because I thought it called for 4oz, not 8oz like the list says...

 

[uss2defiant]

sorry. I don't know.
maybe someone who's a tech can comment.

 

[Billwill]

Download the 2002 KJ Service Manual here...gives you the theory of operation and a fault-finding guide:

Index of /manuals/Jeep/KJ

 

[CoreyH]

Download the 2002 KJ Service Manual here...gives you the theory of operation and a fault-finding guide:

Index of /manuals/Jeep/KJ

Why when I go to the parts store they do not have a listing for a high pressure switch and a low pressure switch? But they have the clutch switch...
There is no way to test these switches at park and idle because everything works right. It's only when accelerating that it starts messing up, and has to be in gear. In park and revving up the engine it still works perfect. In Drive and accelerating then the pressures flop. I cannot find anything online to help diagnose that problem. It's aggrevating

 

[uss2defiant]

i really don't know anything about this problem but the first on the list from the fsm was the accessory belt or serpentine belt if i am not mistaken.
how's the auto belt tensioner?

 

[Conundrum2006]

Reason I ask is because I thought it called for 4oz, not 8oz like the list says...

Should start by saying I didn't look at the linked page, this is going off memory from replacing my compressor in the commander earlier..
I think the compressors themselves are something like 4oz of pag and 8 for the entire system. Each stop in the line (like evaporate, dryer, condenser) holds an once or so. The FSM I read had instructions for adding the correct amount for each replaced part in the line.




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[blackhawk]

Hi everyone. Good topic. I have same problem that Corey, the same symptoms.

I have noticed this also in ralenti with +2200 rpm (waiting time about 15 minutes). But not all the times.
When Libby did this, I just bypass the a/c cycling switch and the compressor engaged immediately. Actually want to buy the a/c cycling just to do a test.

Corey, maybe you can bypass and have these wires placed near to you , take a ride and try when your compressor disengaged .

 

[Billwill]

Again, at idle the a/c works perfect. Low pressure is right at 38psi and I pressure is actually 192. It's only when it's driving that the pressures start to swap and low pressure jumps up and high pressure drops.

How do you know that the pressures are changing while driving?

Do you drive with the pressure gauges connected up and inside the cabin for viewing?

 

[CoreyH]

Yes, my hoses are 6ft long so I ran then inside so I could watch them.
Blackhawk, I have bypassed the switch and with the gauges hooked up ran inside the cab the pressures are all over the place. The low pressure still rises and the high pressure still falls for a few seconds and then goes back to normal for a few seconds and the cycle continues. Only the compressor is constantly running.

I thought maybe the low pressure line may be the culprit but the more I think about it, if there was a partial clog, wouldn't it be acting up all the time?
I may just break down and buy a new compressor. I've exhausted everything with nothing that works.
Can't just sit at idle for cold air