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.

T.C. Mann wrote:

> 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.

www.aircondition.com has forums about auto A/C.

R-12 expansion valves seem to adjust well enough automatically for
R-134a, but pressure cycling switches need to be adjusted for about 4
PSI less low side pressure. I don't know about the suction throttling
valve found in some older Chrysler compressors.

T.C. Mann wrote:

> 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.

www.aircondition.com has forums about auto A/C.

R-12 expansion valves seem to adjust well enough automatically for
R-134a, but pressure cycling switches need to be adjusted for about 4
PSI less low side pressure. I don't know about the suction throttling
valve found in some older Chrysler compressors.

wrote:

>
> T.C. Mann wrote:
>
>
>>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.
>
>
> www.aircondition.com has forums about auto A/C.
>
> R-12 expansion valves seem to adjust well enough automatically for
> R-134a, but pressure cycling switches need to be adjusted for about 4
> PSI less low side pressure. I don't know about the suction throttling
> valve found in some older Chrysler compressors.
>


The valve in question (Evaporator Pressure Regulator, or EPR valve)
should be thrown in the trash when converting an old Chrysler compressor
to R-134a. A thermal clutch cycling switch should be added to the
system to cycle the compressor based on evaporator temperature.
Actually, it works just fine if you wrap the cycling switch's thermal
capillary tube around the suction line as close to the firewall as you
can get it. Its amazing, but the system may well perform BETTER on 134a
than it did on R-12 simply because the EPR valve has a tendency to start
throttling the system back WAY before the evaporator gets down to the
freezing point.

But this system already has a cycling clutch and (most likely) a C-171
compressor anyway, so it has no EPR valve. It may be the high pressure
cut-out switch tripping prematurely (if its got one).

T.C. Mann wrote:
> 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.

That high side pressure seems low.... what's the condenser outlet line
temp?

Jim