AC question with gauges

[Milkman00]

Hi all,

04 Liberty 6cyl.

I did my first AC job ever. I have avoided AC for a very long time, mainly because I didn't know much about it. I wasn't going to pay a ton of money to fix my broken compressor, so I thought this would be a good time to learn.

Got a new compressor, dryer, and orifice tube (couldn't believe I had to do the whole line). Anyway, the job is done, the system was vacuumed out, filled and ready to go. Start it up, AND IT WORKS!!! I have AC. For a little while.

As the car is sitting there idling (20 -30 minutes), with the AC on the outside air setting (not recycle), and I have the gauges hooked up. The pressures are right about where they should be for the temp today (high and low) which is about 250 high and 50 low (89 degrees). The AC compressor will stay fine. After about 20-30 minutes the compressor will start cycling.

At that point the high side drops to about 200 and the low side creeps up. Each time the compressor cycles, the low side comes down, but not as low as it did last cycle, until finally the low side is too high and it won't come on at all.

I let the Jeep sit for a while, come back, start it up and everything works perfect again until the pressures start fluctuating.

Any suggestions?

 

[tjkj2002]

Over or under charged.

The sticker under the hood gives a specific amount of R134A that needs to be in the system by weight.Unless you added by weight you have to much or too little.

Those cans you buy at autoparts stores falsely advertise the actual weight of the R134A inside the can since they also include the all the other junk you don't want in you're AC system(stop leak).

Plus if the AC compressor went bad internally and sent trash into the system you must replace the AC condensor and evaporator also and flush the remaining lines very well.By design you can not clean out(flush) any AC condenser or evaporator and has been that way for 25+ years.

 

[Milkman00]

Over or under charged.

The sticker under the hood gives a specific amount of R134A that needs to be in the system by weight.Unless you added by weight you have to much or too little.

Those cans you buy at autoparts stores falsely advertise the actual weight of the R134A inside the can since they also include the all the other junk you don't want in you're AC system(stop leak).

Plus if the AC compressor went bad internally and sent trash into the system you must replace the AC condensor and evaporator also and flush the remaining lines very well.By design you can not clean out(flush) any AC condenser or evaporator and has been that way for 25+ years.

The old AC bearings were going bad in the compressor, so nothing bad should be in the lines/condenser/evaporator.

I used the plain old 134a cans that don't contain the extra junk you are referring to.

How can I tell by what the gauges are doing if it is over charged or under charged? I assume there has to be a way to tell without just emptying the entire system again, vacuuming out again, and refilling again?

 

[tjkj2002]

The old AC bearings were going bad in the compressor, so nothing bad should be in the lines/condenser/evaporator.

I used the plain old 134a cans that don't contain the extra junk you are referring to.

How can I tell by what the gauges are doing if it is over charged or under charged? I assume there has to be a way to tell without just emptying the entire system again, vacuuming out again, and refilling again?

No way to tell how much you have in the system,only way is to evac,vacuum,and add the correct amount by actual measure weight(actual R134A only using calibrated scale).No way to tell by #'s on a gauge as to many variables exist that can alter what the true psi readings need to be.

 

[uss2defiant]

Did you weigh the cans to determine how much you put in the system?

Sounds like it could be a bad compressor.
Im not a tech so best get it diagnose properly.

If you google ac auto troubleshooting, youll see charts but like tjkj2000 said, lots of variables.

 

[J33Pfan]

I would add more to the low side little by little -checking the gauges. to get te system cold. dont over do it. and check for leaks.

i hope you already added the proper compressor oil to the system.

 

[Milkman00]

Previously I guesstimated the correct amount of remaining can (26oz total system capacity, so 2 cans plus "a little bit".

Ok let's start again. I am going to have the system evacuated again. Also I went and purchased a digital scale today.

Two questions

1. If I zero out the scale with a full can on it, and fill the system until the scale shows -2oz, is that right since the other cans will be 12oz?
2. Will I need to put new PAG oil in the lines, after I vac it?

 

[uss2defiant]

just weigh the can before and after. no need to zero it.

I'm hoping you did put the appropriate amount of oil when you replaced the parts.

Also I'm hoping you have a system to properly evacuate the refrigerant in the system.
You're breaking the law otherwise.

Since I'm assuming you'll have a pro machine to do this properly, you should be able to see how much oil was pulled from the system.

 

[Milkman00]

just weigh the can before and after. no need to zero it.

I'm hoping you did put the appropriate amount of oil when you replaced the parts.

Also I'm hoping you have a system to properly evacuate the refrigerant in the system.
You're breaking the law otherwise.

Since I'm assuming you'll have a pro machine to do this properly, you should be able to see how much oil was pulled from the system.

I had the system evacuated by a shop the first time, but I don't know how much oil was pulled. Is it fair to say that if I have it evacuated and flushed this time, there would be 0 oil in the system? I will do that this time if I need to.

As far as the scale goes, I just want to make sure that 2 ounces of weight = 2 ounces of volume if that makes sense.

 

[adamkrz]

1-when you removed the old compressor you should have checked how much oil was still in it and add that amount.
2 - When charging refrigerant into the the system - you should break the vacuum with only refrigerant from a purged hose otherwise you introduce non - condensables into the system from the hose which create problems.