How does the AC Expansion valve work?

[johnnewcomb62]

Not an AC expert and for some reason since I have gotten the system charged up the low side seems perfect  but the high side

just keeps climbing?  I looked at the expansion valve and don't see anything like a normal capillary tube type where the temp is

monitored by it and opens and closes the expansion valve?  All I see is a little disk looking thing on one end of it where it attaches

to the evaporator.  So I am wondering if it may be not opening does anyone know how it should work?  This is a 1999 c2 and just

wondering what actuates it if anyone knows please.

 

Thanks in advance,

John

[Ahsai]

Any paying member can access this document, which will answer all your a/c related questions.

 

http://www.renntech.org/forums/files/file/1663-after-sales-training-climate-control-systems-diagnosis-repairpdf/

[johnnewcomb62]

Hey Ahsai  thanks, got most of those documents already on file.  I also found a great deal of info

just tooling around different forums most say its built in on these particular valves so its not visible

outside.  But thanks anyway!!

 

John

[Ahsai]

Hi John,

 

Yes, there's nothing on the outside of the expansion valve. As you charge (refill) via the low pressure port, the pressure will increase on the high pressure side as well so that's normal. The valve actuation (regulation) is all done by the internal parts of the valve.

 

Are you experiencing problems currently with the a/c or you're just curious of how it works?

 

BTW, the document in the link above, pdf page 16 explains how the expansion valve works and pdf page 87 shows the normal high and low side pressure as a function of ambient temperature.

Edited July 30, 2015 by Ahsai

[johnnewcomb62]

Yes what I have is the low side is about in the correct range 70-ish and at first the high side seems ok but here in Alabama right now temps are in the high 90's so I have some fans blowing on the condensers to try and portray going down the road at a moderate speed but he high side is going off the chart over 400 so I cut the

air off cause I know that is way to high.  So just trying to figure out if the expansion valve is not working properly.  That what the old rule is if the low side is fine and the high side is high there is a blockage of the orifice or in the cars case maybe an issue with the expansion valve.

 

Thanks,

John

[Ahsai]

Agree that 400 PSIG sounds high for 90F ambient. I wonder if you have overcharged the system. I think the best will be to do a full evac, vacuum and refill and go from there.

[johnnewcomb62]

You read my mind, we did the evac and weighed the refrigerant back in and then took a hose pipe and run water over the

condensors and vo'la!!! got it. The high temp and maybe it was a little overcharged,and maybe the need for the hose pipe to be run on it, so whichever it was all cleared up and we now have cool air!!!

Thanks,

John