AC expansion valve stuck open???

[GreenWater]

The AC in my 87 944 started to not work one day while the car was idling, but would work fine when the car was driving (higher RPMs). This continued and got worse, until one day the AC stopped working all together. So it seemed to me that the compressor went bad.

I just installed a new compressor (and oil), and a new drier.

I also found the slow leak it had, someone pinched an o-ring on the top of the compressor, and now it has no leaks.

Everything was going good until installing the refrigerant.

Only a little went into the system (way too little).

And here is what I have now.

Low side static 80psi
High side static 80psi

Low side running 80psi (AC clutch IS engaged)
High side running 80psi

The compressor was replaced with a brand new unit and the clutch IS engaged.

I'm not totally new to AC systems but I'm no expert at all.

From what I read it seems like the expansion valve is stuck open, since I'm getting NO pressure differences when the car is running and clutch is engaged. All it's doing is just rotating the refrigerant through the system.

Does this seems right? I want to make sure before taking the system apart again and buying a new expansion valve.

Thanks

[v2rocket_aka944]

did you open the valve from the gauge/hose to the ac line?
do the schrader valves work?
are you sure the refrigerant is actually going in...

[GreenWater]

Good question.

Yes, there is refrigerant and pressure actually in the AC lines.

I closed the valves for the gauges and cleared the gauge hoses of pressure. Then attached them to the car and that's how I got the readings. So it's not from the refrigerant in the gauge lines. (I was wondering this too)

Yep, schrader valves work fine too.

[Bradical]

Just to preface, I am a professional commercial HVAC technician and instructor. The expansion device on the pre 85.5 and the 924S is a thermostatic expansion valve, not sure about the later cars but I think it's the same.

Anyway, the only thing that is going to cause the TXV to be wide open is if the sensing bulb, which is attached via a transmission line to the power head of the TXV, is not mounted to the suction (return) line leaving the evaporator that leads back to the compressor. If it is not attached it is sensing the warm ambient air and driving the TXV wide open. That will be the only problem that could cause the TXV to remain open as opposed to being closed. (Edit- What I mean by that is that all other problems will result in a stuck-closed symptom)

If you check the bulb and it is attached, look elsewhere. Your symptoms sound to me like bent or damaged reed valves in the compressor, causing no pumping action, if the clutch is in fact working. But, you could get lucky and it it be a simple fix like just mounting up the TXV bulb

[GreenWater]

Thanks for the advise.

I just removed the TXV from the system and it was, very securely, attached to the return line.

Since the compressor is a new unit, not rebuilt, I wouldn't think the compressor is bad. I don't even know what else to check.

Is there a way to check the TXV?

Thanks

[Bradical]

Submerge the sensing bulb in ice water while the system is running and it should close right up. If the gas in the bulb/power head is lost, which is a completely closed, non serviceable independent charge, the TXV will fail closed. There is an inlet screen that will prevent debris that somehow may have made it past the drier from entering the valve assembly and result in a fully closed symptom as well. The only opening force for the TXV is the pressure from high temperature building up in the bulb and forcing down on the diaphragm to open it, hence why I say they don't fail open.

[Bradical]

The only time I have ever observed no pressure difference across a running compressor was due to valve failure in the compressor. Even when I found a system with no expansion device installed at all there was still a significant difference in pressure (just horrible efficiency). Just my $0.02.

[GreenWater]

Thanks for all that. I will try the ice water thing.

Is there a way to replace the valve in the compressor. I'm great with mechanical stuff, just not AC stuff. I just don't know if they are repairable.

Is a valve failure something that's visible when it's removed?

[Bradical]

Not really, the compressor valves are basically thin metal reeds pinned to a plate on either side of the assembly. They can be bent by the unintended pumping of liquid refrigerant through the compressor, either an extremely excessive oil charge or liquid floodback. Maybe in this case, poor assembly? Taking the compressor apart is something I wouldn't recommend just because it's hard to get them resealed again

If you pull the compressor back out and put your finger over the suction inlet and turn the compressor by hand you should be able to tell it's pumping. It'll push/pull air.

If it's working, then replace the TXV- I can't rationalize what would cause it to be stuck open at all, but if the compressor pumps, it's a safer bet I suppose!

[Bradical]

https://www.instagram.com/p/vMmW04uZeF/?taken-by=bradical924

Here is what the valve plate looks like.

[GreenWater]

I think I might have added a little too much oil maybe.? When I replaced the compressor I added a little less than 2oz to the compressor, since the company that I bought the compressor from said I needed to drain the oil that was in it, and fill it. It just seemed like a lot to me. Could that have done it?

Since the system is open right now I will try spinning the compressor by hand and see if there is suction.

[GreenWater]

I'm ok with opening up the compressor, at least as a last resort. Is the valve replaceable? Or can it be flipped over or straightened?

[Bradical]

That's possible. If it was totally drowning in it, or if you poured it in the discharge instead of the suction, it's possible. I don't know why they would tell you to replace the oil unless it is like an NOS R-12 compressor.

Is your rotary 914 the one I saw on BaT recently or are there more than one mad genius out there? Also, I'd like to add that I am basically an unpaid central florida sales rep for Only944, I love you guys and refer you to 944 folks all the time at PCA events!

Repairing the valves? Never heard of anyone doing that before. You will see that they are separated up a few thousands off of the plate. If you do that sucessfully I will build a shrine to you out of respect. Ha!

[GreenWater]

Thanks for the support, I really appreciate it! And the help with this.

I poured the oil in both sides. I read online that it didn't matter what side I poured the oil into. Is that really bad?

LOL, no, that was not my 914. Mine is STILL 50% finished but I've been working on it recently and I'm hoping to finish it sometime soon.

I just realized that link is a video. It looks fairly easy to open the compressor up. And if it's metal, it can always be fixed. If they are bent I WILL try to fix it. I really have nothing to lose right?

[GreenWater]

I removed the line that comes out of the compressor, and plugged the hole with my thumb and rotated the compressor. There was both suction and pressure (when I spun the opposite way). So the compressor is still good?

I poured most of the oil in this same hole when I filled it. The larger hole, exit hole, where the low side port it.

I'm going to try the ice water trick now.

[Bradical]

Compressor sounds good then.

The part you would submerge in ice water is this this curly bit on the end... A cold temp drops the pressure in that small capillary tubing and releases the downward force on the pin from the diaphragm and causes the valve to close. You'd want to do this test while the system is charged/running and watch the operating pressures.

[GreenWater]

Yeah, that's what I was setup to do, but I think I figured it out.

It looks like the schrader valve on the low side was NOT !!!! working. And based on what I did I think I know why I was getting the readings I was.

I'm going to get a new adaptor/valve tomorrow and see for sure.

I was getting no refrigerant into the low side and the valve doesn't seem to be working at all.

[Bradical]

Ahh jeeze, well thats an easier fix.

[9FF]

I'm impressed you got the expansion valve out, I thought the factory started with that part and built the rest of the car around it. Took me ages just to find it.

[GreenWater]

LOL, yeah hopefully.

I feel stupid for messing up the readings in the beginning and then it skewed everything else I did after that. It made me do a lot of extra work, but I learned some new things, so it's not all bad.

I am having a heck of a time getting the coil clipped back to the return line. How hot does that line get? Can I zip tie/Electrical tape it on there? That would be SO much easier.