Expansion valve ? with rear air
05-05-2010, 03:02 PM
#1
Race Car
Thread Starter
Expansion valve ? with rear air
86.5 the front expansion valve seems to be blocked pressure is rising like a bomb. My question is should I replace both the front and rear or can I just do the front one for now?
05-05-2010, 04:37 PM
#2
Rennlist Member
I had the same issue last year. I replaced only the front at first, then found the rear was leaking and lost all my R12. I'd say if it's over 5 years old, you might want to be safe and replace it (and seals). They are pretty cheap.
05-05-2010, 04:39 PM
#3
Chronic Tool Dropper
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Lifetime Rennlist
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Tampa--
High pressure in the high side is sometimes caused by a failed/plugged expansion valve, but realistically those failures are extremely rare unless you have frag'd something in the system at some point. Or used the wrong oil and have jelly. The more common cause is not enough cooling on the condenser, like lack of airflow or too hot or some combination.
A stuck expansion valve can give you very high high-side and low side pressures when measured at the factory ports. You can get the same reading sfrom overcharging the ssytem, BTW. A plugged expansion valve might have low low-side pressure indicated too, depending on which side is plugged.
To your question-- Yes, you can replace just the front expansion valve. The rear expansion valve is isolated by a solenoid valve on the pressure side until the solenoid is opened by the rear AC controls.
High pressure in the high side is sometimes caused by a failed/plugged expansion valve, but realistically those failures are extremely rare unless you have frag'd something in the system at some point. Or used the wrong oil and have jelly. The more common cause is not enough cooling on the condenser, like lack of airflow or too hot or some combination.
A stuck expansion valve can give you very high high-side and low side pressures when measured at the factory ports. You can get the same reading sfrom overcharging the ssytem, BTW. A plugged expansion valve might have low low-side pressure indicated too, depending on which side is plugged.
To your question-- Yes, you can replace just the front expansion valve. The rear expansion valve is isolated by a solenoid valve on the pressure side until the solenoid is opened by the rear AC controls.
05-05-2010, 04:47 PM
#4
Race Car
Thread Starter
This is my brothers car and seems to have a fairly new compressor. I vacuumed it down and placed the correct amount of R-134 in it. It does not cool and I don't exactly remember what the pressure reading was it's been a couple of months. But I do remember it climbing very high, no telling what is in the system but the car sat for a long time. The restriction point is possible the expansion valve thats what I was told, Condenser fans are fine.
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05-05-2010, 05:16 PM
#8
Shameful Thread Killer
Rennlist Member
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Has the car ever cooled right since it was converted? If there were traces of R-12 left in the system and PAG was used with R-134 it prolly got gummed up.
At this point, since we have no idea what's going on inside, it's kind of smarter to basically start over now.
New front and rear exp valve, new dryer, clean the comp out and put POE oil in, then seal it and pump it down. If it holds, start adding the refrigerant. Who knows, it may work again. Personally, I would go back to R-12 and change oil. POE oil is a kind of solvent and it will dissolve some of the oil mineral oil if it was in there.
At this point, since we have no idea what's going on inside, it's kind of smarter to basically start over now.
New front and rear exp valve, new dryer, clean the comp out and put POE oil in, then seal it and pump it down. If it holds, start adding the refrigerant. Who knows, it may work again. Personally, I would go back to R-12 and change oil. POE oil is a kind of solvent and it will dissolve some of the oil mineral oil if it was in there.
05-05-2010, 07:12 PM
#9
Three Wheelin'
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Yes, R134a for a retrofit, as this is, should use ester oil. If PAG oil was used, then, as mentioned, it's a problem.
BTW, was the dryer changed? It really should have been. If you've got a lot of old junk in the system, you may end up clogging expansion valves easily.
If the expansion valves are still original, then there's probably a benefit to replacing them anyway, just to have R134a-rated valves in place. What you could do, to keep things simple and a bit cheaper, is replace the front one and its seals. You can then run the system with the rear air off (which will block off that section of the system by closing the solenoid valve under the passenger seat). If you have a leak in the rear air system, you'll still leak there, but if you have a bad expansion valve back there it won't be an issue if you're not using the rear AC.
FWIW, I converted my '88 to 134a few weeks ago, and it's fine. I also had my previous 928, a '93 GTS, converted to 134a and ran it for several years, even in Florida, and it worked fine. I don't see such a strong argument for not using 134a in these cars... especially with the cost and environmental impact of R12.
BTW, was the dryer changed? It really should have been. If you've got a lot of old junk in the system, you may end up clogging expansion valves easily.
If the expansion valves are still original, then there's probably a benefit to replacing them anyway, just to have R134a-rated valves in place. What you could do, to keep things simple and a bit cheaper, is replace the front one and its seals. You can then run the system with the rear air off (which will block off that section of the system by closing the solenoid valve under the passenger seat). If you have a leak in the rear air system, you'll still leak there, but if you have a bad expansion valve back there it won't be an issue if you're not using the rear AC.
FWIW, I converted my '88 to 134a few weeks ago, and it's fine. I also had my previous 928, a '93 GTS, converted to 134a and ran it for several years, even in Florida, and it worked fine. I don't see such a strong argument for not using 134a in these cars... especially with the cost and environmental impact of R12.
05-05-2010, 09:21 PM
#10
Race Car
Thread Starter
I have done 3 cars so far including compressor rebuilds. I always change out the R/D and new seals just this one has symptoms I never saw before. Since it's my brothers car and he lives a little way from me I like to get it done right the first time, and the labor is free.
Thanks for the feedback, parts have been ordered.!
Thanks for the feedback, parts have been ordered.!
