r12 manifold gauges - can it be used with r134a?

[jrobie79]

so I found a killer deal on craigslist for an A/C filling station, with a 3CFM vacuum pump for only $50. It has the manifold gauges, however it was designed to fill r12 systems, can I retrofit the manifold gauges themselves to accept r134a canisters? It hooks up fine to my A/C ports (not converted to r134a fittings) but I want to fill it with 134....any ideas?

I already refurbed the entire system, o rings, IIRC 1991 models already had barrier hoses, expansion valve, new condenser, new fan, etc...the only thing I didn't change was the compressor (I put new o-rings and all new seals in it however).

I want to go the r134 route just to troubleshoot the compressor as I'd rather not waste any r12 I have just to find out the compressor is junk.

[Das Delfin]

r12 gauges don't have any readings for r134a. I would just pick up a cheap r134a manifold from HF. Or better yet, rent everything from autozone for free.

(but also get those old gauges because that sounds like a great deal!)

My point is you are already converting your car and know that r134a operates at higher pressures than r12. So you are going to have to do some translating there to get everything right. Why make it harder by using the wrong gauges?

For what its worth I just replaced my compressor with a rebuilt unit. It's common for these old compressors to have worn of failed clutches and coils. This is what happened to mine and it's something you pretty much can't buy anymore. I found this shop in TX who offered to resurface my clutch and set me up a new coil for $75. And entire compressor rebuild would have been $135. I made a thread about AC work and there is a link somewhere in there about it

AC stuff is so complicated and expensive anyway, if you have any doubts about your compressor, just replace it. If you have a Denso unit a Four Seasons 57352 is the replacement if you want to buy a new one from rockauto etc.

[jeffnhiscars]

Not 100% clear on your plans but you do realize if you are switching from r12 to r134 that you have to thoroughly flush the system of old oil and replacement it with PAG

[jrobie79]

the system is 100% clean right now, I want to load it up with r134a to verify if the compressor works....if it does, I'll keep the r134a (assuming the performance is what I want), if it doesn't but there are no leaks, I'm going to put r12 back into it once I install the new compressor.

[Das Delfin]

Your issue with that is you have to change the kind of oil you run. They use two different oils which are not cross compatible, so if you want to go back to r12 after finding out r134a doesn't work as well on your r12 compressor, you'll have to flush out the system.

If you have access to a machine that can do all this, then I don't see why not.. but if not, you're going to pay more in labor having this done than you would just buying a new compressor and throwing it on. That's the concern

[jeffnhiscars]

this^^

If you used mineral oil which is required for r12 you cannot put r134 in it. If you used PAG you cannot let r12 near it. Ester is supposedly compatible with either but I have no idea whether you can just switch refrigerant and reuse it without doing a flush/drier etc.

Propane works as a refrigerant as well although I promise eventually your car will explode, but it might work for test purposes. Again no idea about oil compatibility. Check out nitrogen as well

[Das Delfin]

Chrysler and GM are introducing cars with R1234yf, which is propane-based. However, when Mercedes was testing, they discovered that when the refrigerant along with its oil was sprayed onto a hot engine, it exploded. Ie if you get into a head-on crash and your A/C finds its way onto your motor, you're fucked. That's American car companies for ya

As a side note, as I found out today, the Four Seasons came preloaded with PAG46, which doesn't work with the R12 I wanted to use. Also I found out my lines had a weird red/brown dust inside. Which means my expansion valve is probably shot. The R12 TXV is now NLA so I'll have to do a retrofit... Today was a bummer.

I'm not sure if older compressors which have been rebuilt for R134a would run it at peak efficiency.

[jeffnhiscars]

R12 compressors are not "ideal" for running r134 due to differnt operating pressures but there are lots of these systems that do a fine job (including Alice and the black Cabrio I just rescued).

If you are determined to stick w r12 I do have an expansion valve that's available. It just needs a good cleaning.

[Das Delfin]

I don't have my heart set on R12. I was hoping for a relatively easy way to get my A/C working. Now that I see it's going to involve an entire overhaul, I'll go R134a