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Low Side Too Low, High Side Good

94RX-7 on Tue September 03, 2013 6:52 PM User is offline

Year: 1994
Make: Mazda
Model: RX-7
Engine Size: 1.3L
Refrigerant Type: R-12
Ambient Temp: 95
Pressure Low: 15
Pressure High: 225
Country of Origin: United States

System fully overhauled due to leaking compressor shaft seal. NEW compressor installed. Both heat exchangers were flushed with mineral spirits and thoroughly dried. All lines were flushed. Factory style receiver/drier is no longer available from Mazda or aftermarket so new hoses were made to adapt a drier of a similar volume from a different application. Expansion valve was also replaced. TXV is NLA from Mazda and the aftermarket has no listing for this application. An expansion valve for a 1999 Miata was used instead. System was evacuated for several hours then charged with 2 12 ounce cans of R-12. Under-hood sticker calls for 28 ounces of refrigerant. Several years ago I tried putting this much into the system and the high side pressures indicated a clear overcharge. Factory service manual calls for 21.2 oz. of refrigerant. Sight-glass was clear as the last ounce or two was charged into the system.

Performance of the system at idle is poor, and at 1500 RPM performance is mediocre. Above pressures were taken at 1500 RPM, blower on high, recirc on, windows down. The suction line coming out of the firewall was ambient temperature or slightly below. Factory spec for 95 degrees at the blower inlet is 28 low, 213 high.

My theory is that the evaporator isn't being fed enough refrigerant by the TXV. Do I have a bad TXV? Is it impossible to successfully use one for a different application, even though it physically fits just fine? Is something else amiss?

Chick on Wed September 04, 2013 11:58 AM User is offlineView users profile

The problem could be the expansion valve.. A valve for your RX7 is still available in the aftermarket sections..
One from a 1989 to 1998 MPV is the same, miata is not... Check with the sponsor of this board at [email protected] for price and availability on that and the drier (Both made by Global, so he should be able to get them) hope this helps.
BTW, four seasons still list the driers..?? Get the right parts, do it right you'll do it once....

Ackits.com

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Edited: Wed September 04, 2013 at 12:24 PM by Chick

94RX-7 on Wed September 04, 2013 1:01 PM User is offline

Global being another name for GPD? If so, GPD's part number of 3411239 for the expansion valve is not correct for this application. My valve has an external equalizer tube, and a bulb type sensor, not the "pigtail" sensor shown for that part. The board sponsor has a listing for an expansion valve for this car that attaches to the lines and port correctly, but the sensing bulb is too long. It was a royal PITA to fit it into the evaporator case on another RX-7 I worked on.

I chose the Miata valve because the valve and fittings were dimensionally correct, and compared to the other options that were dimensionally correct, the Miata valve had the lowest superheat. I have no idea what Mazda originally spec'd the superheat at for my car.

I see only one listing for a drier for this car from 4Seasons, and it isn't the one I need. Mazda had two different systems made for these cars. One by Nippondenso, the other by Zexel. I have the Zexel system.

Quote
Get the right parts, do it right you'll do it once....

Believe me, I'd love to. Trouble is, nobody sells them anymore.

Chick on Wed September 04, 2013 1:22 PM User is offlineView users profile

can you post a pic of the old expansion valve? maybe someone can help a little more..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

94RX-7 on Wed September 04, 2013 1:44 PM User is offline



Chick on Wed September 04, 2013 1:55 PM User is offlineView users profile

Aftermarket expansion valves don't always have the bulb.. A lot of the new ones have the twisted tube like the GPD valve, you just clamp that end part to the evap same as the original, and insulate it good..
I don't suggest this route, but if nothing was wrong with the old valve, you could use it again if you can't find a new part that works.... But I have used the pigtail type in place of the sensing bulb before with no problem...You can always check with Mazda to see if the 98 MPV has the same part number as my listing shows.. If so, they might be able to get the valve for you??

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Chick on Wed September 04, 2013 2:07 PM User is offlineView users profile

Checking a little further, you might try crossing a 91 RX7 with yours.. All that I find have the newer winding on the end, including AcDelco.. But none cross to the Miata, so I'd go with the GDP if you use a new one, and just clamp the end tight to the tube and insulate.. Looks likea case of trial and era, but it appears the closest match would be the GPD or older RX7, you're using R12 anyway...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Cussboy on Wed September 04, 2013 2:32 PM User is offline

Quote
Originally posted by: 94RX-7



If your original expansion valve looks like this one (your top picture), sure looks a lot like the expansion valves used in 1986-1993 Mazda trucks:




94RX-7 on Wed September 04, 2013 2:53 PM User is offline

Quote
Originally posted by: Chick
Checking a little further, you might try crossing a 91 RX7 with yours.. All that I find have the newer winding on the end, including AcDelco.. But none cross to the Miata, so I'd go with the GDP if you use a new one, and just clamp the end tight to the tube and insulate.. Looks likea case of trial and era, but it appears the closest match would be the GPD or older RX7, you're using R12 anyway...

Unfortunately, neither the GPD nor the 1991 RX-7 valves are externally equalized....so they won't work.

94RX-7 on Wed September 04, 2013 2:58 PM User is offline

Quote
Originally posted by: Cussboy
Quote
Originally posted by: 94RX-7






If your original expansion valve looks like this one (your top picture), sure looks a lot like the expansion valves used in 1986-1993 Mazda trucks:



According to 4-Seizin's web site, that valve has #6 and #8 fittings. I need M16xM20.

94RX-7 on Mon September 16, 2013 6:33 PM User is offline

Tore the system apart again, replaced the valve with one for a different application (1994-1997 Miata) and now it is cooling like it ought to. I didn't get any debris out of the previous valve, so I suspect it was simply defective from the factory.

Cussboy on Mon September 16, 2013 10:28 PM User is offline

Quote
Originally posted by: 94RX-7
Tore the system apart again, replaced the valve with one for a different application (1994-1997 Miata) and now it is cooling like it ought to. I didn't get any debris out of the previous valve, so I suspect it was simply defective from the factory.

Great.

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