A/C problem advice requested - '84 Westy

[fxr]

Having eventually succeeded in getting the A/C to work as well as can be expected (which is pretty good, all things considered) a couple of years ago, last year it began to lose performance - but that seemed to mainly be down to a slow leak .

This year, the whole interior was removed for a comprehensive rust appraisal (some small repairs needed) and re-paint, new window seals etc. I took care to
seal off the ends of the A/C hoses that connected to the evaporator.

I've just replaced the interior, and am in the process of refilling the A/C. Yes, it held vacuum steady overnight just fine (the previous small leak must have been an evaporator connection) and with the compressor off the first can of Envirosafe went in just fine. Turned on the compressor, with shop fan in front and revs at ~3000, and tried to get more Envirosafe in. The pressure on the low side just kept going up and up, with the high side just above it. Perplexing. Stuck vanes? Oh - low on oil maybe and now buggered?

I had a spare compressor, so decided to swap it in. A much better result, with the high side getting up to 150psi pretty rapidly on the second can - but the low side just kept going up as well - hovering around the 75psi mark. Output temps were 15-20°F below ambient.

Nothing I could do seemed to change this, and it didn't want to suck in any more Envirosafe.

So what problems, idiocies on my part, or parts failures could cause this? I'm thinking perhaps the TXV (expansion valve) itself has failed in some way?

I'd be very grateful for a few pointers.
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[jlrftype7]

Sounds like the Expansion Valve is stuck open. If it was closed, you’d go into a vacuum on the low side while running. See if a tiny piece of crud got loose and is jamming it open. Doesn’t take much, a bit of stray desiccant from the receiver-drier, broken o-ring bit..etc.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[Howesight]

I agree that the symptoms suggest that the expansion valve is malfunctioning. Recall, however, that refrigerant pressures are dependant on temperatures, both ambient temps and system demands, so without knowing those, the high side pressure cannot be accurately analyzed.

The low side pressures, however, can be analyzed. When the compressor is operating correctly and the TXV is working as designed, low side pressures should never be in the 75 psi range - - 29 to 32 psi is more appropriate. This is the smoking gun that points to the TXV in your case.

Even when you block off hoses in an opened AC system, the PAG oil in your system will act as a desiccant and absorb huge amounts of ambient moisture. This effectively ruins the charge of PAG oil in your system which should be fully flushed out. Moisture contamination of the PAG oil causes the PAG oil viscosity to change and allows the captive moisture to freeze in the TXV. The gummy water-logged PAG oil can make your TXV malfunction.

If you flush the whole system (I even run flush fluid through the compressor in such a case, filling it and draining it twice), and replace the TXV, you will probably get a good outcome.

Here's a tip I recently learnt by happenstance when rebuilding my wife's Audi S6 AC system: You can install the entire refrigerant charge without ever running the compressor. The Audi only has a high-side service port because Audi uses a sophisticated extraction/filling machine for servicing these cars and it measures the correct fill and pushes it in the system under pressure. So, I could not use the DIY low-side "vapour suction" approach to filling the system.

I mimicked the Audi dealer's machine by starting with a 29 in hg vacuum in the AC system, then charging with an inverted can of RedTek into the vacuum. This sucks in the first can. For cans 2 and 3, I did the same, but applied moderate heat to the RedTek cans with a hairdryer. This raised the pressure in the RedTek cans to around 80 to 100psi, which easily pushed the liquid refrigerant into the 65 degree F system which sat overnight in my garage until a cool September morning. This cannot be done as easily if the car is over 75F. At 75F, the system pressure in the Audi with compressor off is around 55 to 65 psi, meaning you would have to apply a lot of heat to the RedTek can, which tests the structural limits of the can.
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'86 Syncro Westy SVX

[Farf]

[fxr]

Good answers - they mesh with my thoughts on the TXV.

The oil previously in there was an Ester oil - my understanding is that isn't hydroscopic.

A complete flush will be a bit of a pain - but worth it I guess! I'll also research which TXV is a good replacement.

I have a feeling this might be a project to take my time over - and as we're going away in a couple of weeks for a two-week road trip Mrs fxr will not want the van disassembled again beforehand.
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[jlrftype7]

[fxr]

OK - but I'm told this will have to wait until after our trip. I don't know what model of valve is in there, it was replaced when the Subie conversion was done for an R134a compatible one. I'm not sure that's necessarily a good thing...

I don't even have a picture of it at the moment. So let this lie dormant for a few weeks, then we'll have another go at getting this working well again - ready for Baja in Feb.
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300