Automotive Air Conditioning Information Forum (Archives)

94RX-7 on Wed May 22, 2013 3:09 PM

Year: 1994
Make: Mazda
Model: RX-7

There are no aftermarket listings for the expansion valve for my car. None. Even the one that our dear sponsor has listed is incorrect. My questions are:

If I can find a valve that fits and the superheat is off 2 or 3 degrees either way from what the factory specified, does it really matter?
Do I need to go on a quest to measure the superheat my current valve is operating at and make sure I match it exactly?

Is there really that much variance in the superheat of the valves that are out there, or is pretty much everything set to run at say 4 degrees?

TRB on Wed May 22, 2013 5:51 PM

Post up a pic of the one you need and I see if I can find it.

A degree or two is not going to be a deal breaker as things vary in automotive a/c systems. But if you can get the correct item it is best.

-------------------------

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Contact: ACKits.com

NickD on Thu May 23, 2013 5:54 AM

How come we don't fool around with superheat, wet bulb temperatures, and all that with MVAC, but do with HVAC, least I don't, maybe I am dumb.

Did this car come stock with R-134a or did Mazda bribe the EPA like GM did with a bunch of SUV's back in 1994 still using R-12. But R-134a was new to the manufacturers as it was to us, did have a learning curve. Some Japanese vehicles took another four years to work out some problems. The condenser was the major one.

Anyway, sounds like you are having a problem, what is it?

94RX-7 on Thu May 23, 2013 9:19 AM

Quote
Did this car come stock with R-134a or did Mazda bribe the EPA like GM did with a bunch of SUV's back in 1994 still using R-12. But R-134a was new to the manufacturers as it was to us, did have a learning curve. Some Japanese vehicles took another four years to work out some problems. The condenser was the major one. Anyway, sounds like you are having a problem, what is it?

It came stock with R-12 and a parallel flow condenser. For 1995 Mazda switched to R-134a with a slightly increased condenser fin pitch.

The problem I'm having is finding the right TXV. I want to be as sure as I can that I'm matching the factory TXV as closely as possible.

Installed ACKits P/N 31-12105 on a friend's car last summer and the sensing bulb was way longer than the original and it was a PITA to fit into the evaporator case. This was part of a full system teardown, flush, and compressor replacement, as well as some modifications to adapt the aluminum lines to use a different receiver/drier since the drier for that system is NoLongerAvailable. The performance of that system was decent, but not as cold as it should be. Didn't have the instrumentation necessary to measure superheat.

94RX-7 on Thu May 23, 2013 9:26 AM

Quote
Originally posted by: TRB
Post up a pic of the one you need and I see if I can find it.



A degree or two is not going to be a deal breaker as things vary in automotive a/c systems. But if you can get the correct item it is best.

P/N 31-12105 fits, but the sensing bulb is way too long....and who knows what factory superheat is. The bulb should only be about 1.25" long at the fattest part.

Here's a pic of the only markings on it:

94RX-7 on Fri May 24, 2013 3:34 PM

Alright. I've managed to find listings for various valves that should mechanically fit. Now it is down to picking the right superheat.

The superheats I've found are -.5 (a factory R-12 car with a variable displacement compressor (is it called supercool when negative? LOL)), 1.5, 3, and 5. The -.5 is out since that would seem to guarantee slugging. So that leaves 1.5,3, and 5. These are all going to, presumably be charged with R-134a as the working gas in the bulb. The applications they are for are all in the R-134a era.

My big question is this: Can I go with the 1.5 to get the coldest evaporator possible, or is that a bad idea since I'm going to be running R-12 and that slim of a margin with R-134a as the working gas in the TXV will put me into slugging territory when R-12 is the actual refrigerant in the system?