80SC factory air running R134A

[targa80]

Well I was finally able to charge the converted factory A/C with R-134A yesterday and I was able to get 45 degrees from the center vent with my generic analog thermometer at 2000 RPM's. The last time the system was running was in 2002 before I took the car off the road. Back then, it was running R-12 and the temps were always mediocre. I remember having it on full blast and it was barely comfortable before a crack in the line near the rear condenser connector that goes to the compressor hose leaked all of the freon.

I have spent a considerable amount of time reading as much as I could on the different options:
1. Staying with R-12
2. Converting the factory stock air from R-12 to R-134A
3. Converting to R-134A while adding some new parts, compressor, additional condenser, expansion valve, low high shut off switch to the existing system
4. Scrapping the whole shebang and going with a state of the art after market R-134A system that are available and are highly praised on this board.

In my case it all boiled down to how much is the cost. I was unable to justify scrapping the components from the existing system since they were still functional, granted not the best system, but still functional. My option was to fix what was broken, flush the system, add ester oil and a new dryer and charge with ~36oz of R-134A. The ~36 oz. was based on 85% of a R-12 system from Porsche (~42 oz.).

This morning the static pressure was at 75 psi and the ambient air was at ~70 degrees. By the time I got around to starting the car up and running the A/C the ambient air was at ~80 degrees, Low pressure was at ~40 psi and the high pressure was at ~235 psi. At 2000 RPM's the vent temp was around 45 degrees. I disconnected the gauges buttoned up the car and took it for a drive through the neighborhood for about 15 minutes. the vent temp dropped to ~40 degrees.

Overall, I am happy with that. Plus I gained the benefit of learning and doing something that I had not done before with a minimal out of pocket cost.

I will add the following disclaimers:

1. This system is still +34 years old except for a new dryer, replacement dryer/evaporator hose, new front condenser fan motor, and the metal (not aluminum) R-134A adapters. This means, I have no idea how long the system will stay as a functioning A/C system, but then again, I can hope that my maintenance will pay a dividend, only time will tell.

2. Yes, I am still using those non-barrier hoses that will eventually if not by tomorrow morning leak out all of the refrigerant.

3. No, I did not change the expansion valve because it is still functional as far as I know. granted, it may not be to spec for R-134A but then again it is metering the Freon from the high side to the low side.

4. No, I did not install a low/high cutoff switch because I can never ever remember when my condenser became so cold that it froze over and caused a high pressure situation to blow a seal. If I do get a leak and my little analog thermometer indicates that the temp is not dropping I will shut it down and investigate the issue.

My total out of pocket expense was $377:

$50 - Manifold gauges (R-134A)
$99 - 2.5 CFM vacuum pump
$22 - Drier
$75 - Drier/evaporator hose
$50 - Condenser repair (Braising)
$12 - R-134A adapter fittings
$ 9 - Ester oil (8 oz.)
$15 - A/C flush (32 oz.)
$45 - R-134A (three 12 oz. cans)
$ 377 - Total

[Damon in STL]

Good Job!

I just picked up a '75 911 and I'm getting ready to "re-install" the a/c system. A number of the interior pieces came with the car in a box.

I'm not sure what is good/bad at this point. Right now most of the electrical is disconnected. This will be my first task to sort out.

Luckily I just installed a new compressor in my BMW 540i.....so I now have all the tools to do the job!

Cheers,

Damon in STL

[schoward]

Good job. I drove my 81 which is converted to r134a 275 miles on Saturday through a twisty road day and it was great to be able to flip on the a/c when things got too moist (occasional drizzle) and also just to manage the cabin temp. Had to turn the temp knob down in the late afternoon as full cold was too much. I generally don't use the a/c a ton, but blasting through hilly passes with a comfortable cabin was pretty nice and kind of needed with an 8 hour day behind the wheel. Certainly made the day more enjoyable.

[targa80]

Damon,

I would recommend doing a vacuum on the system while it is out of the car. Use the old drier since you will be taking it apart agajn before installing.

[wwest]

Originally Posted by targa80

.

2. Yes, I am still using those non-barrier hoses that will eventually if not by tomorrow morning leak out all of the refrigerant.

4. No, I did not install a low/high cutoff switch because I can never ever remember when my condenser became so cold that it froze over and caused a high pressure situation to blow a seal. If I do get a leak and my little analog thermometer indicates that the temp is not dropping I will shut it down and investigate the issue.

My total out of pocket expense was $377:

$15 - A/C flush (32 oz.)

Should you discover that those non-barrier hoses do leak R-134a refrigerant in spite of the EPA and DuPont stating otherwise, may I make a suggestion, espouse my position, theory?

Install a Red Dot 71R7500 trinary switch. Use the third element to power the cabin heat blower, and maybe even "snake" a wire all the way up front to front lip condenser blower control so it only runs "as needed".

Then. Use a 10-15 minute TDR, Time Delay Relay, to supply power the third element post engine shutdown..


Maybe the Germans were smarter than we think.

Many MVAC systems of "our" era, and even up to the early 90's, included an HPRV, High Pressure Relief Valve, ~500 PSI, to reduce the probability of system component damage, hose bursting, etc, when/if the high side pressure exceeded the system design specifications.

My 1992 Ford AeroStar R-12 refrigerant, had such a valve, a 500 PSI vent to atmosphere pressure relief valve mounted to the compressor discharge side.

500 PSI..?

R-12, "vent to atmosphere"..???

Yes, the EPA requires that systems equipped with an HPRV being retrofitted to R-134a have a PS installed with a 325 PSI compressor shutdown setting.