Just getting my new 4 seasons expansion valve out of the box and noticed is says 134a on it. I’m going back with my old rv2 and r12. Will this make any difference? I’ve still have the old valve but it not be used in many years.

As far I know , the difference (aside the seals), is the pressure adjustment. Can be readjusted but for the price of the piece doesn’t worth the readjustment effort. On my car thought made the R134 “upgrade” on my stock system, including the expansion valve without any readjustment and worked really nice. But I will install a correctly adjusted R134 unit (same, 4 seasons unit that probably you got ) when reassembling my car.

About reuse the original one, well, my car was with the AC without any use by maybe 15-20 years by the original owner (and I refill the system maybe in 2005) and when I made it to work again, still with the R12 before the R134 upgrade, worked nicely.

If it has no adjustment, it will overfeed a bit with R12 if its a fixed 134a valve. If it's adjustable, you will have to turn it in a bit probably. You should check superheat, which is the difference in temperature of the gas at the outlet of the evaporator(wear the sensing bulb is mounted) and the saturation temperature (measured using the low side guage pressure and 134a pt chart). Superheat on automotive is typically 8-10 deg F

I have not installed it yet and it is not adjustable. I’ve been told ten different stories on this subject. It makes sense to me that the valve should be different. The girl at the sales department at Old Air could only state what’s in her notes. “It will work”. The molecules are different and the pressure is higher in 134.

Do you have your original expansion valve? If it's in good shape I would re-use it.

Some times the bulb will develop a leak then you are SOL

I do have the original. It was still on the car but the short discharge hose was the only hose in the car. It was probably removed early on so it has been exposed for a long time. I still have several parts cars with the complete systems still intact that I could use but they have been dormant for many years I found an NOS one on eBay for not much more than old air wanted for one of their 134a valves. I got a 134 marked valve on rock auto for $25. I just don’t want this thing to fail right off and waste my R12.

New (not NOS) r12 parts are still available at parts stores if you are worry about still use the original one. Just request for it. I’m sure 4Seasons still makes them. When I got my expansion valve and dryer I asked to Rockauto to be specific for r134 (for the later upgrade I was to make) on parts request. They told me the PNs for 4 seasons between R12 and R134 parts were diff by just 1 number. Let’s say! R134 PNs were 3xxxxxx and R12 were 2xxxxxx

…or something like that. That was long time ago.

So ask the dealers or straight to 4seasons

Thanks for that info. I’ll try to contact four seasons. Rock auto does not show one for R12. A 134 valve may be close enough to work but every other part is different so it has to make some different. I do know that when I converted my 84 crew Cab to 134, it did not work very well with 134 even though I upgraded the condenser.

Rockauto doesn’t mention on their website if what they sell is for any of the refrigerants (or didn’t back when I bought) hence why I contacted them and got that answer. I guess they asked to 4seasons and replied me with the answer got from 4seasons

Well. I got the NOS R12 expansion valve in with all the correct size o rings from multiple places, evacuated the system and pressurized it to 100 lbs with nitrogen. I found two small leaks with the nitrogen at the schrader valves. I replaced them repeated and they held. I filled it with liquid gold, R12 to the proper amount and it comes out of the vents at 34-38 degrees.