Expansion Valve Adjustment on Dodge Van After Switching to R-134a

Hello,

This past weekend I converted my '84 B250 Dodge Van from R-12 to
R-134a. I rebuilt the compressor using R-134a compatible seals,
replaced the receiver/dryer, changed the oil, installed the proper
fittings, pulled a vacuum, etc. I used 75% (by weight) of the regular
R-12 charge. The manifold readings were 165 PSI and 35 PSI (high/low)
with an ambient air temp of 82 degrees.

The system seems to be cooling fine now. The only difference that I
noticed is that the compressor seems to be cycling on and off more
rapidly than when it had R-12. I have heard that sometimes the
expansion valve need to be adjusted after changing to R-134a. Is it
possible to adjust the expansion valve on these vehicles and if so,
what is the proper procedure? Thank you.

 

Don't see a parallel-flow condenser on this list. Means you will never get
really good system performance. It'll never come up to the level of a
properly-functioning R12 system in the same vehicle, especially in high
demand situations (slow speed, hot days). On the other hand, if you don't
make high demands of your A/C system, perhaps your threshhold of
"acceptable" cooling is less stringent than mine.

At what engine RPM? 165 on the high side is low.

No such adjustment is possible.

 

try adding a few more ounces of 134 pressures are a little low

 

the TEV or TXV more than likely needs adjustment when changing refrigerants.
You may also need to change the thermostatic charge element. ( the bulb and
diaphragm assembly ) You could check superheat and subcooling figures to
figure out if the system is charged and the TXV is working correctly. I
have no idea what those figures would be for an automotive system or if a
replacement element is even available. To learn more about TXVs go to
www.sporlan.com - on the other hand if it has acceptable cooling and the
pressures are not too high, leave it alone and enjoy life.

mark

I have heard that sometimes the

 

This can *sometimes* be done on stationary installations -- TXV adjustment
and thermostatic charge element replacements are not possible on MVAC, at
least not on this system.

 

Thats what I pretty much figured. The only possibility is that a similar
valve for a different refrigerant was used on a later year/vehicle. One of
the big problems with individual retrofits is the lack of information and
the difficulty of working with the aluminum tubing used in the system. (
its a fairly simple matter to r&r components with a copper / brass based
system)

 

ok, scape the idea of a few more ounces

 

And I would add "not necessary." The required operating ranges for both
R-12 and R-134a are well within the operating range of the TXV, so it
just does its thing and doesn't care which refrigerant is flowing
through it.