Carpokes Porsche Forum

Tom wrote: Mon Jun 29, 2026 3:32 pm

shft22 wrote: Mon Jun 29, 2026 11:10 am Replaced all four o-rings, did all the good stuff to get the system as it should and she is cooling ok. It was 91F outside when I took this picture.

Thank you all for your help.

IMG_9586.jpeg

Good work! Glad it was that simple!

If you are the type to fixate on things for no practical reason, know that you could get it another 15-20 degrees colder still.

Similar compressor in the 928, AC converted to R-134a, cruising west across central California on 46 headed towards the coast. Anti-freeze switch jumpered to support an un-tinted black car in Los Angeles. Cabin setpoint at 72º F, Ambient 85º F, center vent 20º F.

You can get the system really really cold, like freeze your fingers on the steering wheel cold; it's certainly possible with some care and diligence.

So if nothing turns into a pumpkin at 20F, why does the system even have the freeze-over switch? Frostbite risk? Now I want to bypass my freez-over switch so I can finally get started on that super-conductor stand-alone system I've been mulling.

Wow this inspires me to get my ac fixed. But I better fix the power steering, new vacuum leak, and bad gas first.

Belgian951 wrote: Tue Jun 30, 2026 3:09 pm Wow this inspires me to get my ac fixed. But I better fix the power steering, new vacuum leak, and bad gas first.

Hey this is a god place for inspiration, so far I have been inspired to do the following;

vacuum leaks -- Disconnected vacuum for fuel tank vent -- Will remove all lines in the future
leaky fuel lines by the tank -- replaced hose with home made AN hoses
radiator fans not working -- Fixed wiring going to resistor and replaced relay
Half shaft -- replaced all four CV joint
transmission drain plug -- old plug had no walls to hold a wrench, replaced with new one with magnet
transmission fluid -- easy after replacing the drain plug
rear shock frozen -- replace with new koni
dash lights -- all LED
Turbo gauge -- Repaired wire at DME
wiper motor -- replaced with new one
intercooler -- had a hole replaced with used good unit
A/C -- replaced controls, compressor seals
Dash cracks -- Installed dash overlay
Seats -- Installed seat covers -- Looking for sports seats at a reasonable price.

But for now since the car A/C is working I will enjoy driving it for a bit to see what other issues come up. Besides is way too hot to work in the garage.

Tom wrote: Mon Jun 29, 2026 7:03 pm So if nothing turns into a pumpkin at 20F, why does the system even have the freeze-over switch? Frostbite risk? Now I want to bypass my freez-over switch so I can finally get started on that super-conductor stand-alone system I've been mulling.

Who knew 80's tech would be the key to you taking over the world!?

It definitely looks like my system needs TLC. The coldest I see at the vents is around 50°F

Important to manage expectations on car AC performance. Relative humidity, and specifically the related dew point have a huge effect on vent temps. Lowering the air temp 1º below that dew point number takes about 1000 times the heat removal as it does to move the sensible heat the last degree down to that dew point number. A soggy 30% RH day in the desert climate in most of California, or the high desert of central Oregon where we are now, is way different from a soggy 90%+ RH day in Tennessee or most other southern states. So 20º or even 40º vent temps may not be attainable on those days there. Look at the dew point temp where you are, and decide if it's close to the center vent temp you are seeing. If so, you may need to increase the system heat transfer capacity by 1000x, give or take.

The anti-freeze switch is there to help avoid ice buildup on the evaporator. Important in humid conditions and on longer drives. The perfect switch setting would be right at freezing, with minimum deadband. The mechanical switches have a bit of hysteresis, and that only gets worse as they age. There was a discussion in the last couple years about using a smarter sensor-plus-relay for the duty.

Even a little ice buildup acts as an insulator, heat transfer drops as the fins clog, air vent temps go up even faster as more ice builds up.

There's a great case for cleaning the evaporator too. Commercial AC coil cleaner aerosol works well to get accumulated dust off the fins in the evaporator. From the HVAC aisle at Home Depot. Rinse thoroughly. Install a cabin air filter before the evaporator if you don't have one already. Airborne dust and crud make a nice mud-mat when they contact the condensing moisture droplets on the evaporator.

There's a market opportunity for cabin air filters for our 'vintage classic' Porsches like mine that didn't have them from the factory. I -really- need to get a 3D printer for such things.