I recently replaced the heater core in my 99XJ. The AC was working, but I chose to replace the evaporator core while I was in there (it appeared to have been replaced previously). I purchased a new accumulator as well. I had the system evacuated in advance.

I've read a lot of opinion about PAG oil when replacing individual components. I hadn't quite made up my mind about how to proceed, but figured as a first step, I'd drain the oil from the evaporator core and accumulator and record those amounts. Figured it would give me a good starting point.

The evaporator core had less than 1/2 ounce of oil and the accumulator had no measurable oil. Again, these were from a working AC system.

I'm thinking at this point I should drain the compressor and split the capacity requirements between the compressor and accumulator.

I'd appreciate any suggestions as to how to proceed.

Thanks!

 

The only way to be really sure of how much oil is in the system is to drain the compressor and flush the system to get the old oil out, then add in the amount specified. (Usually you'd put 1/2 the total in the compressor and the other half in the receiver/drier.) PAG oil very readily absorbs atmospheric moisture so adding the oil should be the last thing done before buttoning up the system and drawing vacuum.

There are rules of thumb for adding oil when replacing individual components. That will usually get you close but is not always going to be correct:

http://www.underhoodservice.com/ac-o...essor-failure/

(It is probably better to have a little too much oil than too little. Too much will reduce cooling capacity. Too little will fry the compressor.)

 

You're right.

I'm wondering how it can be that there's no oil. I understand that with a new fill (post flush) you add 1/2 of the amount to the compressor and 1/2 to the accumulator but I thought that oil circulates through the system when it is charged and operating. Is that accurate? I'm curious whether I'm going to find any oil in the compressor.

I don't know how long it had been since the system was last apart. I bought the Jeep in September last year and used the AC for probably less than a month. I also used the defroster all winter. I had it evacuated in the spring before procrastinating on the heater core repair all summer.

Perhaps I should start compressor shopping.

 

It's possible it was low on oil when you got it, though the oil is dispersed throughout the system and it's hard to say how much is going to come out of any specific component. The "safe" thing to do is to flush the system out and put in a new compressor with the correct amount of oil. If any doubts about the hoses those should be replaced as well. (These are all components pushing up against 20 years now.) You can be reasonably sure then it's not going to grenade on you and will work for a while.

The cheap way of course is just to add some oil by rule of thumb, button it up, and go. Or you could split the difference and flush/fill using the old compressor. The result may be OK or it may be a disaster waiting to happen. (How lucky do you feel? )

Keeping the AC working on an older vehicle is a challenge!

 

If I'm not careful, I might learn something. Back when I was fiddling with cars & trucks regularly, we didn't have any stinkin' AC! My prior AC work has either been "dump a can of refrigerant in it" or "change a compressor and take it to my buddy to flush/charge."

I popped the compressor off tonight and drained it. Again, less than 1/2 ounce. The good news is that what little oil there was is pretty clean and clear. No signs of metal. There is some dye from either previous troubleshooting or someone simply grabbing the can with dye from the parts store.

At this point, the only disaster would be having to change the evap core again.

 

Sure sounds like that AC system is low on oil. It's a good sign that there's no metal contamination but it's still going to be something of a crap shoot using the old compressor if it's had insufficient lubrication.

Bear in mind that if it craters you'll probably wind up having to replace the condenser and evaporator. I'm pretty sure both are parallel-flow on XJ R134a systems (the condenser for sure) and those can't be reliably flushed out if there's debris from a failed compressor.

I'd probably be leaning towards compressor replacement if it were mine. I really would not want to have to replace the evaporator twice. (Or even once if I didn't have to!)

 

Thanks. Again, you're right. I will be in Vegas soon... maybe I'll try my luck...