Ricardo Vega II

Converted AC from R12 to R134a and ordered o-ring kit, receiver/drier and expansion valve from Pelican. Installed parts on Sunday and also cleaned lines with alcohol before doing install of parts and also removed oil and installed new oil as well. Put everything back and worked great Sunday for the few hours left in the day. Monday I go to work and no freon, blew hot air. Had put dye for detecting leaks and only found a slight one at new adapters at high side. Tightened up with a 5/8's wrench a bit more and then put gauges again today and filled up with freon again and pressures we saw were 30-32 and 200 but air is warm not cold at all! Stuck trying to figure why? Any recommendations? Checked heater valve and that works fine. But stumped on why no cold is coming out. Thanks!

Ricardo Vega II
1987 928 S4
97,000 miles

MainePorsche

Heater valve on the right way ?

SeanR

Did you vacuum the system down before putting R-134a in it?

Randy V

Are you sure the AC compressor is being energized?

That should be the first step.

Do you have rear AC?

Ricardo Vega II

Hey guys! Thanks for responding and it was related to the heater valve. Even though it would close water would still pass. Hoses were super hot that went in to the heating core. I looped it out of the heating core into the engine which removed the heat. That obviously helped a lot but we also found we were lacking freon as well. So now I have a super cold AC.
One last question and this has to do with how cold is cold for this system? My AC is only front vented and not rear. If I put a thermometer on center console what would be optimal? What would be super cold? And how low can I possibly get down to?
RVII

69gaugeman

There is a chart in the WSM that shows what temp should come out of the center outlet depending on outside temperature.

dr bob

With proper charge and everything working correctly (including the freeze switch) your center vent temps should cycle just above freezing (say 40ºF) with engine above 1500 RPM, ambient below 90ºF, and something less than saturatd air in the cabin, inside fan set on second speed. Industry guidance says 40-45º of temperature drop is sufficient. My converted '89 car with freeze switch bypassed will make 17-19ºF at 95º ambient in desert-dry SoCal motoring. Additional humidity puts a lot of extra load on the system, as the moisture (humidity) is condensed by removing heat from the water. Without getting too deep into the 'why', remember that removing moisture effectively lowers the "dew point" of the cabin air, giving the sensation of cooler air as it does a better job evaporating perspiration.

Just a casual warning that the polyolester oil used with R-134a will help you discover any o-rings you might have missed.

Ricardo Vega II

Thanks to everyone that chimed in. Dr Bob, might you be able to email me or call me so I can ask you more questions about that freezing relay that I can bypass? I do live in the west Texas desert where humidity rarely gets above 20% but heat gets at about 100 on an average day. Would like to find out more about your setup if possible. Here's my email vectortrainingsystems@gmail.con or my number is 9154904233. Thanks!
RV2
1987 S4 Black/Red

SeanR

It would be better for the community if you posted your questions here so those that also have questions, can get them answered. The reason for this forum is the sharing of knowledge.

GrumpyFinn

Yes Please, following from S. Florida

Ricardo Vega II

Cool! And I understand, well my question was going to be about bypassing that relay. What would be the end result if it cause problems? Driers would get clogged? O-rings would fail sooner? Compressor would give up the ghost sooner? Living in the high desert, 3,900 feet and average of 2.5 inches of rainfall a year would not stress mine out too much but just want to be sure. Thanks and let us all know Doc!

RV2
1987 S4 Black/Red
97,000 miles

MainePorsche

The freeze switch is just that - not a relay. Where you are you could probably safely bypass it. Under the black cowl in front of the windshield is where the switch lives. It is a sliver box with two wire contact points. You can simply bypass it, just remember it is a safety check point in the system.

Ricardo Vega II

Ok sounds good, I'll try it out today and let you guys know what blows up or what freezes. Just messing with y'all. I'll keep you posted though, thanks!
RV2
1987 S4 Black/Red

dr bob

The risk is that condensation on the evaporator coils will turn to ice before it drains out the bottom of the housing. I've had the switch bypassed for a dozen years or more, OK in the desert-dry SoCal climate and a relatively short drive cycle. Motoring up the central velley a few weeks ago, with ambient temps over 100º, it was blowing cold enough to freeze fingers on the wheel. But... Every half hour or so I needed to switch the AC off to thaw out the evaporator. The air stays "cool" from all the ice in there, at least for a while after turning the compressor off. Then it starts to get warmer and more humid in the cabin as the evaporator thaws out and sheds water to the hot incoming airflow.

Bottom line I guess is that the "perfect" compromise for most would have the freeze switch bypassed for the first 15-20 mins of compressor operation, then revert to normal freeze-switch function after that. You'd have full system capacity available to draw out the heat-soak heat, yet avoid the downsides of the iced-up evaporator and the thawing-out process. I've given thought to how best do that, perhaps in concert with an external compressor relay near the freeze switch. Challenge would be getting power up there safely. A compromise could be made with a simple time-delay relay for those with the upgraded compressor relay already installed at the control head.