328 AC switch over

Has anyone switched over their 328 AC system from R-12 to the R-134...any positives/negatives

my mechanic recently mentioned this as a possibility. price range is large depending on whether hoses need to be replaced, which apparently could require removing the gas tank for access

thoughts appreciated

 

the advantages to switching are:
1] you can get r-134 cheap and top off leaks yourself
2] environmental

the disadvantages seem to be everything else (resulting temps, conversion cost). Opinion from previous threads is is just doesn't blow as cold as r-12, and the r-12 system is not great to begin with.

hose replacement is not necessary, however, I'd disconnect the compressor hoses at both ends and blow some brake cleaner through them with compressed air to clean out accumulated ester oil sludge. One thing to check, however, is hose damage where the hoses loop up over the gas tank. The hoses tend to rub against the chassis and eventually wear a deep enough divot to blow out (mostly the high pressure side).

The drier needs to be replaced, and the compressor may or may not need to be depending on whether it's been changed out in the past and the seals are compatible with pag oil.

search the old fchat archives. The 308 system is the same, so all those comments apply.

 

R12 systems have mineral oil, not ester oil.

While new R134a systems use PAG oil, Ester (POE) oil is required for retrofits because it's compatible with the seals, etc. used in R12 systems.

The GM dealers are now doing R134a conversions under factory directions. They are completely doing away with R12 refills. My GM dealer converted my '91 Olds custom cruiser wagon to R134a last year. It blows as cold (45 degrees at the vent) as it did with R12.

I WAS SURPRISED TO LEARN THE FOLLOWING:
GM does not recommend flushing the lines, apparently it dislodges stuff that otherwise would stay in place. GM only requires changing the dryer if the system has been open to the air for more than a few hours( changing it is insurance). Only o-rings that have been disturbed must be replaced. It's been established that the R12 lines & seals do not need to be replaced unless they're leaking. Apparently the mineral oil permeates the inner layers of the lines/seals & forms an effective barrier to R134a.
The compressor does not need to be changed unless it's faulty or has leaky seals.

If you have the YORK style compressor, then the mineral oil in the crankcase should be sucked out thru the fill hole & replaced with POE oil until oil comes out of the fill hole.

If you have the smaller cylindrical compressor, the mineral oil must
be drained out & measured, then replaced with an equal amount of POE oil.

Also add an ounce of POE to the high side service port.

By federal law, you must do the following:
1)After adding the oil, the system must be evacuated to remove all traces of moisture & R12 before adding any R134a.
2)replace the service ports with R134a ports &
3)install the R134a retrofit lable saying the system was converted. Service shops will not touch a converted system w/o the ports & lable as they can't afford to risk having their R134a equipment contaminated by R12.

My '82 308 was converted when I bought it. Recently recharged the A/C. It was blowing 46-48 degrees at the vents on an 85 degree high humidity day.
(BTW, prying out the highly restrictive 3x8 A/C vents seems to about double the flow of cold air! With them out I had to turn the A/C temp down because it was getting chilly inside the car on that 85 degree day.)

(BTW, The Harbor Freight venturi air pumps can not pull a good enough vacuum to remove moisture unless the temp is close to 100 degrees(don't ask).

 

oops on the ester oil vs. mineral oil vs. pag...never can keep it straight :-(

interesting comments, verell. I get around 38-40 degrees in the vents on my 328 with r-12, though.

sludge in the lines I'd still go after. Even if you leave out some kind of solvent, blowing air through will push out most of the remaining oil. It tends to collect in the low pressure line. Of course, I had an extreme case of crud buildup which actually preventing the system from circulating properly - it wouldn't even suck in r12 to charge the system.

otherwise, do what verell says. for the cost of draining/filling the compressor and replacing the fittings, plus the cheap r134, you can give it a shot and see what happens.

on the other hand, you gotta weigh in the mechanics bill if you aren't doing the work yourself. Assuming you aren't leaking, then simply topping up the r-12 system every few years is probably more cost effective.

fwiw, I'm going to convert the next time I have a reason to open the system...but I rarely use the a/c, so if it's a few degrees less effective, I don't care. It's more convenient to have r134

 

Hmm, my guess is that your system was badly overfilled with oil. Real 'crud' (ie: debris of some kind) will almost immediately clog up the expansion valve & stop things from working at all.

Excess oil is quite common on older owner maintained cars because of the freon cans sold with an oil charge. Owners figured thay ought to top up the oil when they topped up the system so they'd buy the freon w/oil. Of course there's no way for an A/C system to loose oil, so it eventually over-filled the dryer & compressor, eventually ending up in the lines & blocking them.
Excess oil is one of the reasons that dryer replacement is recommended when converting to R134a. That way you know that there isn't a lot of oil in the system.

If you have to blow out your lines, do not use compressed air, that injects far too much moisture into the system, even if the air is going thru a good refrigerated drying system. (Hmm, I think air from one of the new dessicant based drying systems with fresh dessicant would be safe tho.)

Best to use dry nitrogen, or an other dry inert gas such as argon/co2.

 

I did the conversion on mine and switched to a Sanden compressor too.

ONE THING TO NOTE--the 134 system needs to be pressurized a bit higher than the old r-12 system. you will have to run the 134 at a lower pressure (like r-12) and get moderate cooling OR bypass the pressure switch and pressurize to low side of 134 numbers OR find a 134 pressure switch and retrofit.

I did the second because i cloud not find a 134 pressure switch that was a direct replacement. the newer cars 355 etc have them but will require some modifications to make them work.

 

Do the conversion and change the dryer, too.