So with the recent heat wave thats been passing through my area, I thought it would be a good Idea do get some cold a/c blowing in the old swedish.. It's an 88 240.

I know I didn't quite follow procedure for the conversion from R-12 to R-134a, but I figured I kinda just want a cheap quick fix. so I changed the fittings, and put a vacuum on the system.. it holds vacuum really well..
I then added oil, and go to put a charge on the system to get enough pressure for the low pressure switch to allow the compressor to engage.. Upon doing so.. the compressor never engages..
I took the console to find out that my switch was stuck in the off position.. I fixed that and the compressor kicked on..
So again I go to hook up and charge the system only to find that both high side and low side are sitting around 100psi. my buddy tells me that it's probably the expansion valve, stuck in the open position..
I replaced the expansion valve today and tried to charge the system, only to find that the low and high side pressures are still even, sitting around 100psi..
Now correct me if I'm wrong, but it was my understanding that the high side pressure should be somewhere around 200psi and the low side should be around 25 or 30 psi..

Completely stumped.

BUT! the new expansion valve that I installed did get cold and start to collect condensation.. So now i'm thinking maybe a blockage in the evap core??

ANY SUGGESTIONS??

 

That is correct when the compressor is running. When the compressor isn't running you will see the high and low pressures being the same. So is the compressor running when you see the equal pressures?

 

Yea, the clutch engages. but it still registers equal pressure between the high and low side.. Could there be a blockage somewhere? I was thinking there aren't too many things in a standard a/c system. reciever/drier, condenser, compressor, evaporator, expansion valve.. The compressor engages, so we know that works, the expansion valve is brand new, and the reciever dryer you can see the oil moving through the sight glass so I would assume that it is functioning properly.

My next guess would be the evaporator... because the expansion valve gets cold when the a/c is turned on. So maybe there is a blockage in the evaporator that isn't letting things cycle all the way through.

Any thoughts?

 

As you said, you didn't "follow proper procedure". Did you flush the old mineral oil, which does not mix with 134A, out of the system before adding moreoil - presumably ester oil? If not, you have way too much oil in the system for good cooling. The gauge readings sound like you have an insufficient charge, and I'd be willing to bet that you've got air, moisture and who-knows-what in there, too. How much refrigerant did you add? Did you measure it somehow, or just kind of guess at it? I'm assuming that you're aware that the proper charge in a 134A conversion is just 80% of the R12 amount, right? You shouldn't be able to "see the oil moving through the sight glass" if the system is fully charged and you shouldn't be seeing bubbles either. How long did you pull a vacuum? 45 minutes to an hour is pretty much the accepted minimum. Did you change the drier? Not trying to give you a hard time, my friend, but AC work is an area where you really do need to "follow proper procedure" if you want any kind of decent results, "decent" meaning 38-45 degrees out of the center vent when you need it. Sounds like you've got the basic idea down, but you might want to read a bit more and then start over from square one. Good luck with it!

 

Does the Dryer not have a silica bag in it that can bust and clog the lines?

 

Absolutely. It probably wouldn't clog the lines, but it could clog the expansion valve. I've seen compressors that were on the way out (mostly Ford Fx 6) deposit pieces of seals in orifice tube screens, too. Certainly worth checking. A shame to have to do it, since iatotofts said he had just replaced the expansion valve, but there it is...

 

yea, but I would think that i would at least get something out of it.. And I wouldn't think that the system would totally refuse to take any charge because it has too much oil.. and I also wouldn't think that it would cause the high and low side pressures to balance out..

 

So you think I might need to replace my expansion valve again? or my compressor? I feel that since the expansion valve was getting cold that the problem would more than likely be after the expansion valve ie: the evap core. what do you think?

 

I'm wondering how you determined that the pressures were equal to begin with.
Did you have the high side valve open or closed when you took your reading? I'm also wondering where you had the high side line connected to..

You are correct that an oversupply of oil probably would not cause the system to refuse a charge. Gases, fluids, liquids generally flow from an area of high pressure to a lower pressure area. As the saying goes, "Nature abhors a vacuum". If you're showing 100 PSI on the low side, you're going to need more than 100 PSI forcing the refrigerant into the system. You may not have that in the cans you're probably charging from. There a lots of things that can cause restrictions. For example, too much moisture from improper evacuation can freeze in the expansion valve. Probably not instantly though, which makes me suspect the high side valve being open on your manifold.

 

We were using your standard refrigerant pressure guages with the high side line the low side line and the feed line, along with the commercial sized refrigerant tank (about the size of a propane tank).. as far as where I had the high side line connected. If you are looking from the firewall of the car and you see the lines coming out of the compressor the line on the right side is where the high side is connected. And we had the high side open when we took the reading..
my buddy was thinking that I may have a bad compressor because he had similar readings on a porsche he was recharging that he had forgotten to plug the low pressure cut off switch back into. His theory is that the clutch may be enguaging but something in the compressor itself has essentially broken loose/free

 

Wow. My limited experience has been that it's almost impossible to get a conversion fitting onto the high side of the radial compressors. The low side is a little easier...
Joseph knows his stuff...you have to in Texas. Frankly, I do not see how the gauges would read balanced while the compressor was running. If you used ester oil instead of PAG oil, a little mineral oil in the system is no big deal. And changing the dryer? Sure, it's best...but I've done just what you did on a couple of my own cars w/ success. Not long term success, but the car was cooling nicely. How long was the system uncharged? Was the system open to the environment? Cuz I'm thinking your compressor may very well be fubar'd. Hard to say w/o seeing it...let us know your progress.

 

I think you just solved the mystery - the high side gauge should be closed, especially when charging. Let me elaborate a bit : when you open either gauge, you are opening to whatever is in the manifold between the two gauges. The valve is just a door between wherever the far end of your hose is connected and whatever is in the manifold. Think of the gauge as being on the far side of the door. If you close both the high and low side valves, you will still get pressure readings; the only reason to open one is to let something pass one way or other into the system. The high side valve is mainly used for purposes of evacuation and applying vacuum, otherwise it needs to be closed. When you are evacuating or pulling a vacuum both valves are normally open, although in the case of stupid Volvo AC, which has no high side fitting except on the compressor, I normally just pull my vacuum through the low side, with the high side closed. Charging, you only want the low side valve open.

Suggest you hook up your gauges again with both valves closed. I'll bet you get different high/low side readings..

 

i will have to check those and get back to you.. I have some other problems to attend to with the volvo first. Unfortunately

 

It's been a decade but I'm having a/c issues and found your post. Were you able to fix your ac and if so, how did you do it? Thanks!

 

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