I’ve converted from R-12 to R-134a on all of mine, and several other
vehicles. In the US, the conversion kits contain two cans of R-134a, a
3 oz. can of PAG oil (2 oz. of oil & 1 oz. of propellant),
quick-connect R-134a fittings for high & low side Schrader valves, and
a charging handle to fit to the R-134a cans.
If your system has recently worked on R-12, and has NOT been left
exposed to the atmosphere due to a ruptured hose, etc., and you have
NOT had a component failure such as the compressor seizing which can
put debris into the system and plug other components such as the
expansion valve, then conversion is easy.
All you need to do is remove the R-12 (local law may require it being
pumped out by a shop); put a vacuum pump on the system for 15 to 30
minutes; let it sit for an hour or so to see if it holds vacuum; add
the 2 oz. of PAG oil (the original mineral oil will remain in the
system, resident in the compressor sump, condenser, etc. and NOT
removed by the evacuation); and then add ~ 30 oz. of R-134a. I use a
$10 air vacuum pump that is driven off compressed air. If you have air
tools and a compressor, this is a cheap do-it-yourself solution. It
cannot provide as deep a vacuum as a $200-$300 vacuum pump, but it
provides very satisfactory results.
If you have a sight glass on your receiver-dryer, watch for reduction
of bubbles as the R-134a is added. You can add the first can without
the compressor running, to get enough system pressure to make the
compressor pressure switch engage the compressor clutch, and then start
the engine and have the compressor running to add the rest (another 1
to 1.5 cans) of the refrigerant.
Before you evacuate the system, you might be wise to replace the
o-rings at the rear of the compressor (where the refrigerant lines
attach to the back of the compressor) and at the expansion valve at the
firewall, simply because these tend to fail with age. You might also
wish to replace the receiver-dryer, particularly if you have had to
open the system to replace o-rings, hoses, etc., and NEVER leave the
system open to the atmosphere; ALWAYS put plugs/caps on any
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
I’ve placed an order for the conversion kit from R12 to R134A gas
on AC for my 1990 XJ40 Daimler. Anyone with experience as to what
the work entails?
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