hacker-pschorr

I was out for about an hour running the car pretty hard to test the new oil (see the delvac first impression thread). Back in the garage I decide to test my cooling fans (do this from time to time after I blew a circuit - all 100% aftermarket, my own setup). So I let the car climb a bit at idle, watching the temp gauge, turn on the A/C to really test the system. Few seconds later a loud hissing sound, following by the garage filling with white smoke.

Looks like the pressure relief valve on the A/C system opened

Good news is I turned on my fans, coolant temp came right down.

I'll update the oil thread tomorrow when I can drive the car in 85 degree weather to compare to Monday's drive.

dr bob

Eric--

The only "pressure relief valve" I know of in my 928 AC system is possibly a blow-out plug in the top of the drier. All others are DT's of regular system components. I hope your freon chose something inexpensive to vent through.

hacker-pschorr

Was coming from here:

IcemanG17

Hacker
Is your high pressure cutoff switch bypassed? Or maybe it failed..but I thought the failure mode was to turn off the compressor? It should have shut the compressor down before it got high enough to pop anything..like that drier..odd

hacker-pschorr

The rod there next to the tank (no idea the technical terms) is "wet" and I could feel the steam coming from a little black thing that looks like a cap on a tire valve.

If I can find my other lens I'll take a better photo.

Imo000

That could be a pressure port. Can't recall if its the low or the high pressure but under that cap it should look a lot like a regular tire valve (or something simmilar).

Why did you fan fuse blow?

hacker-pschorr

I think my fuse housing was too close to the radiator, so the fuse didn't blow as much as the housing melted that was last summer just after I installed these fans. This was supposed to be a temp setup I have not gotten around to changing. On the first few hot days I usually roll around at low speeds or sit in the driveway and make sure everything is working before heading out of town.

I f*cked up by not turning on the fans with the A/C like I normally do. I like to see if the car stays at "normal" operating temp this way. If it starts to rise I shut down the A/C (usually it stays just fine). This time without the fans pulling heat out of the A/C system.....well this happened. So 100% my stupid fault.

IcemanG17

Hmm
Maybe your fan bypass also bypassed the high pressure switch?? I don't think so but can't read the wiring diagrams good enough to know for sure...Causing an overpressure situation due to excessive heat? Possible....

hacker-pschorr

Ths is on the 81 - main fan is mechanical, I took it off in favor of electric fans. I also pulled the large fan out front. It was broken & I have yet to install a replacement.
I know for a fact this is what happened, it's 100% may fault since I did not turn on the fans. I really need to finish that install with a temp switch.

So consider this thread a PSA - if you install electric fans, make sure they come on no matter what when the A/C is on.

Alan

On my GTS the high pressure switch (right on top of the dryer) is set to 32 Bar - that's 464 PSI !

Thats a lot of pressure - I assume yours is at least similar...

So if the fans are off or if one dies - pressure builds to significant amounts - quite possibly enough to blow a dryer seal/bubble window that may have been sitting there for 25+ years.

On my car that's the H-P port location too - so maybe the schrader style valve is what let go...

Eric - when you put the relay/switch/fuses in again use the dual 40A relays (or better) and surface mounted Maxi Fuse holders - I like them for these ~30A feeds and they are pretty inexpensive.

The ATC fuses are OK but there are very few ATC fuse holders that are good enough for this much power...not even the ones Porsche uses!

Alan

Jim bailey - 928 International

The early car has no high pressure switch...just low pressure and a thermal switch which turns on the a/c fan.

hacker-pschorr

So now I get to find what blew

Jim bailey - 928 International

One time use pressure relief ...blows out it is part off the rec/drier

Randy V

Hey, easy with the techno-talk there, dude!

hacker-pschorr

That's what Jim Page was telling me today - so not too bad.

Is this something you would have used or am I better of to bite the bullit and buy new?
Yea well, hey, I do what I can.

I wish I would have had a camera. Lorelei peaked into the garage just as it blew, filling the garage with smoke. She ran for cover.