Packard Forum Index » V-8 (1955-56)

Anybody know of an air conditioning shop other than original air group in Florida that can rebuild the A/C modulating valve to work with R-134a? Original air group is months out and this is holding my project up. Looking for alternatives.

I hope you find someone and if so, please let us know. I looked for someone doing repairs for mine some years back without success. The place in Fla was not too optimistic the could and also wanted $$$$ to try so I never sent it in. While modulating valves are still used on commercial systems, have found nothing small enough that could come close to that one either in fit or looks.

On my rebuild I wound up with temp control done by adding an adjustable thermostat to cycle the compressor clutch which was the cheap low tech aftermarket method done in those days but almost a norm to save on gas mileage today. My compressor is a Sanden retrofit so built for that cycling clutch setup but have heard pros and cons on whether the original Lehigh compressors can hold up to the continual cycling. If the compressor fails that seems to be another item where there are almost no parts (valves in particular) available.

I took apart an A/C modulating valve and don't see why it wouldn't work with R134a. It's all metal on the inside, no rubber that I can see. Anybody else take one of these apart?

There is a lot more to converting to R134a than just that! To answer your question, I've not taken one apart but have discussed a proper conversion of all components with one of the vintage air shops.

Some people with older AC systems from all mfgs have reported changing to R134a without any major changes while others report nothing but problems -- even after sending their various valves to places that are supposed to rework them to work with R134a. Refrigerant leaks with old components are also an issue.

As far as the modulating valve the calibration is what needs to be changed. There is roughly a 2 psi difference between R12 and R134a at the same 38F or so degrees the modulating valve needs to hold at the evaporator. While the screw on the end of the valve can do the adjustment it takes some time between adjustments to stabilize so there may be a bit of back and forth adjustment and will require good pressure gauges to get it just right. The valve needs to keep the evaporator warm enough not to freeze over but still cold enough to be at the optimal cooling temp -- between 32 and 40F is where Packard wanted it but toward the higher end gives more of a safety margin so the evaporator doesn't freeze. The expansion valve may also need a similar recalibration as it is also pressure operated and could flood or starve the evaporator if not set fairly close.

The bigger issue with R134a conversions is the old stock hoses and fittings. The R134a molecule is much smaller than the R12 molecule and the old rubber hoses frequently let the refrigerant leak as does the flare fittings and the seal on the compressor. Hoses most likely will need to change to new barrier types and flare fittings may need to be opened to have a special sealant applied to the mating surfaces and then retightened. Oil in the compressor also needs to change to one compatible with R134a. If the compressor seal leaks there is not a lot that can be done other than change the compressor to a modern type compressor with internal components compatible with R134a.

What little I’ve learned actually came from the Imperial Club’s posting on the issue so to plagiarize it, here is one of the detailed postings:

Excellent Tips from Tony Dickson:

Both R406A and GHG-X4 (now called "Autofrost", "Chill-it," and other names) are 100 percent legal for use in cars.

As far as using a modern R134a refrigerant (like in a 1995 Neon) with a new dryer, compressor, hoses, etc. here is my experience: You're looking at replacing some components either way, but the switch to R406A is going to require MUCH less expense, MANY fewer new parts, and will yield MUCH better performance and efficiency than R134a. Basically, DO NOT(!) convert your R12 car to R134a or any of the R134a-based refrigerants (FRIGC comes to mind). They are far less efficient than R12 and R406A, GHG-X4, etc. Also, they are HIGHLY incompatible with R12-type oil. They operate at radically different pressures, so calibration of R12 expansion valves won't be optimal. Also, since 134a is so inefficient, one must use larger compressors, condensers, and evaporators to get the same level of cooling as from an R12 system. This is difficult and expensive to do on an existing system, so you get much less cooling with 134a. To convert to 134a PROPERLY so as not to shell any of the components, you're going to need:

a) All new hoses (The R12 hoses are permeable to the smaller R134a molecule)

b) All new seals and O-rings (ditto above)

c) A rebuild of your V2/RV2 compressor (because this compressor design uses an oil sump and pump which cannot be "flushed" of oil like other non-sump type designs, and because 134a is so violently incompatible with 12-type oil, you have to get ALL of the old oil out.)

d) New receiver-dryer with XH7 or XH9 desiccant

e) And you should really purchase a parallel-flow condenser to try and make the system work at least marginally, if not optimally well.

Now let's compare that to using R406a or GHG-X4:

They are MORE efficient than 12, yet it operates at similar pressures, so the expansion valve calibration will remain optimal and your existing condenser and evaporator will function MORE than adequately.

They are completely compatible with R12 type oil, so no system flush or expensive compressor rebuild.

You still need new hoses, because R12 type hoses are permeable to the smaller R406a factions' molecules.

Ditto new seals. (New hose-to-hose and component-to-component seals, you don't have to mess with any compressor or other internal seals).

I should have clarified to everyone as to what I am doing. I'm retrofitting a non a/c '56 Packard Caribbean with a factory a/c system per the instructions posted on this site. Most of the important parts I have are NOS: condenser, evaporator, expansion valve, Lehigh compressor, rubber hoses (bought those back in the 80's before R12 became the boogey man) and have a line on an NOS modulating valve. Evaporator and case are mounted in the car ready to install expansion and modulating valves. Then ready to re-install instrument panel.

I’m doing the same thing in my 1956 but with used parts, not NOS although I may splurge on some if necessary. Do you have the oil filter relocation lines? You’ll need those too as the compressor mounts where the filter is currently located.

The seals and rubber hoses would be of the most concern and likely would have to be replaced with modern material. For my 1965 Imperial LeBaron with dual front and rear A/C, that’s a major undertaking but not so bad on the Packard.

Couldn't find any old or NOS lines for an A/C car. I had to custom make my lines. First, I had to install the compressor bracket with the oil filter mounted to it to the engine (compressor off the bracket, much easier that way). Got about 6 feet of tube, cut in half. Then got new fittings, flared one end and installed fittings on the tube. Installed the one end each in the block and bent the tubes to fit, lastly screwing the other ends into the oil cannister. Took some time but it worked.

For the oil filter relocation lines, I believe I have an extra pair but I’ve not advertised them in the Classified Ads of my site because they are as yet untested. They were made by Classic Tube and if they saved the pattern as I asked them to do, they can make you a set out of stainless if you prefer and which is what I will be using on mine but my extra set is steel.