The early ('63-'65) Rivieras used a
Suction Throttling Valve (STV) instead of a POA valve. These systems
adjust the outlet temperature by regulating the pressure in the
evaporator (using the STV). The STV is adjustable, so it will handle
the different operating pressures of R12 and R134a.
The problem with the STV is that they
are vacuum operated (via the
vacuum modulator, which is controlled by the temperature lever),
and the diaphragms a) tend to go bad, and b) are expensive to
replace. Luckily, the failure mode in the Riviera systems is full
cooling; in the full-size cars a bad diaphragm means minimum
If you're mulling a change to R134a,
consider this: you can retrofit for well under the cost of a full
R12 charge. The worst part of the change is draining the compressor
and replacing the mineral oil (incompatible with R134a) with ester
oil. This will only cost you $5 and some time, and the ester oil
will work with R12 if you decide to switch back.
To make the change:
- Replace compressor oil.
- Install new ports for R134a
- If your system hasn't been working
for some time, replace the receiver/drier. You'll want to do this
even if you're sticking with R12.
- Evacuate system.
- Run your engine @ 2000 RPM, full
A/C, with an auxiliary fan blowing across the condenser.
- Install 75% of a full load of
R134a (if your system uses 4# of R12, start with 3# of R134a).
- Add R134a 1 oz. at a time until
you reach max cooling at the outlets (stick a thermometer in a
vent). When the temperature starts to go up, remove what you just
- Adjust the STV (loosen the lock
nut and turn it in/out) to get an evaporator pressure of 18-23 psi
on an 85 degree day.
NOTE: you will see bubbles in
your receiver/drier with a full charge of R134a. This is normal.
Properly installed, this should get
you to within 3-4 degrees of an R12 system. When you consider the
original cooling specs, that's compatible with (or better) than some
new cars. Of course, you will benefit greatly from a fan shroud and
an operational fan clutch. If you're going to drive in
stop-and-go traffic on a regular basis, I would recommend an
auxiliary electric cooling fan in front of your condensor. It might
not be stylish, but neither are sweat rings in your armpits. You can
fit a fairly large fan behind the grill on those cars. Hook it up to
the A/C clutch switch, and you'll help yourself out every time you
drop below about 35mph.
There are also rumors that R134a is
more likely to leak through hoses due to its different molecular
composition. I don't know if that's true or not, but there are two
- The hoses are so thick that, while
technically correct, it's not a practical issue.
- Even if it does leak, it's a slow
leak, you can replace a lot of R134a for the price of new hoses.
It's like replacing your main seals to stop a slow drip when oil's
.69 a quart.
Free advice (you get what you pay
for): if your system works now, stick with R12. If it doesn't, make
the low budget switch to R134a.