Re: [AMC-list] 1964 Classic A/C problem

[Frank Swygert <farna@xxxxxxx>]

Hmm... let's see what I think... Note that while I've dome some of my own AC service, including charging and converting gases, I'm not an AC pro.

First things first - new compressor and hoses, as well as new expansion valve. My 46 year old valve seems to work fine, by the way (63 Classic). I run a Sanden compressor from a Jeep 4.0L though, but that makes no difference. 

My first thought is that there should be a strainer screen in the inlet (high pressure hose) of the expansion valve. You stated that you flushed the system, but was the strainer checked after flushing? It may be clogged now. 

The check valve is between the high pressure side of the compressor and the receiver/dryer (note: both names are used for the same device/function -- I'll use dryer from now on). It's shown on top of the dryer (built into the dryer?) in the 64 TSM. It appears to be there to prevent "feedback" from the dryer of high pressure liquid or gas in the (unlikely) event that pressure builds in the dryer or high pressure line and overcomes the compressor. I would think the only time pressure could/would leak back is when the compressor stops, and then it should be only gas going back into the compressor. I suppose if for some reason liquid got back in the compressor it could cause damage, but that's highly unlikely. 

Since you mentioned the check valve not being in the 75 TSM, I checked a couple others. I think I found out why the check valve was omitted. The design of the dryer changed in 1973. Dryers with a high pressure input directly down from the top have the check valve. Starting in 73 the dryers have the high pressure input low on the side with the discharge inside the dryer up near the top (tube runs inside to the top). The internal design reduces the chances of a back-feed situation.

You're going to have to discharge the system to check anything now. You should be able to use air pressure to test the check valve. The high side can be up to 300 psi, so I don't think running 100-120 psi of air into the valve will hurt. Blow through the high side first, and if you get air out of the low side try blowing into the low side. Of course you should get no air. It's possible that flushing the system got trash in the check valve too. 

--------
Date: Sun, 5 Jul 2009 20:11:30 -0500
From: "Carter Braxton" <cbraxton@xxxxxxxxx>
Subject: [AMC-list] 1964 Classic A/C problem
To: amc-list@xxxxxxxxxxxx
Message-ID: <20090706011130.B6946326701@xxxxxxxxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset="iso-8859-1"

I'm trying to help out a friend out with the air conditioning on a 1964 Rambler Classic. Someone else did a half-hearted R134 conversion on this car that did not work out. (The dryer had not even been changed.) Symptoms were no cooling and gauges showing the low side going into suction and high side pressure only about 120 psi on a warm, sunny day. The compressor is new and the hoses were rebuilt with the original fittings.

What we have now done is to flush out the evaporator and condenser to get rid of any debris and old oil. (Quite a bit of grunge came out.) A new expansion valve was fitted, the compressor oil drained and the factory recommended amount (7 oz.) of ester oil installed. In order to maintain stock appearance, the original dryer was sent out to be rebuilt. The rebuilt dryer was installed and the system drawn to 30" vacuum for about an hour and a half before recharging with R134.

After all this, the car still has the same symptoms -- no cooling, with suction on the low side and ~120 psi on the high side. Basically it seems like there is a blockage somewhere in the system. I also noticed that there is a check valve going into the dryer. It appears to be integral with the fitting on the high-pressure hose that connects the dryer with the expansion valve, and attaches to a fitting on the side of the dryer.

On my own car I've had the experience of a brand-new defective expansion valve causing this kind of symptom. However, looking at that 45-year-old check valve I'm a bit suspicious of it. How likely is it to be causing this problem? Is it really a necessary component? (My 1975 AMC service manual shows what is basically the same system, but there appears to be no such check valve at the dryer.) If the check valve is needed, are they still available?

--
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
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