405 aircon cutting out

dturbo · Post by **dturbo** » 18 Jul 2011, 19:27

When it's hot (i.e. all the time now) the aircon works for the first couple of minutes and then cuts out. There is a leak in the system but I regass it regularly. Both fans are running. When the ac cuts out the revs rise to 1.5k rpm and the hot air creates condensation of the previously cold ac vents. No button pressing, temp/vent sliding, cursing, switching engine off, etc. will bring the ac back. I have to wait for the system to cool down sometimes 20 minutes, sometimes 40 min sometimes hours even.
While I'm sweating like a pig is there a way to trick the ac to stay permanately on? It's probably detecting the leak or has to work really hard so it's shutting down to prevent damage? I know if I keep it running it will eventually die but I'm willing to give it a go. No climate control which means should be simpler to troubleshoot but having zero knowledge on ac I thought I'd ask here.

spider · Post by **spider** » 19 Jul 2011, 09:44

The pressure switch will cut it off at too low or too high ( ! ) pressure. Although bypassing them is likely to cause damage if the pressure is too low, and potentially a burst if its too high.

DickieG · Post by **DickieG** » 19 Jul 2011, 11:20

When the A/C cuts out are the cooling fans running at high speed? If so then more than likely the system is over-gassed causing the high pressure cut-out to operate. When this happens it does take quite some time for the pressure to subside before it will operate again i.e. overnight. How are you re-gassing the system, a home kit by any chance?

dturbo · Post by **dturbo** » 19 Jul 2011, 12:24

I will have to get back to you on the fans. The system cannot be over gassed as the gas leaks out after a few months and the ac is still cutting out with very little gas left. Can't be under gassed either as it just had a refill. For regassing I just take it to any guy with a gas tank and dials. It only takes 5-10min. I had it done "professionally" a few times with the vaccum/die/etc. for 1 hour but the end result was the same (except for a lighter wallet).
Is it possible that the pressure switch is a fault here?

spider · Post by **spider** » 19 Jul 2011, 14:33

Its possible although I cannot recall one failing, but I guess stranger things have happened.

Its just screwed into the line, I think you'll see it on the offside inner wing area. Bad news is the system will need to be empty (evacuated) to remove / replace it.

addo · Post by **addo** » 19 Jul 2011, 23:52

That's not necessarily bad. I can't see the merits of running a system to destruction.

Flex hoses eventually die; they can be easily renewed using the original hard line tails. Evaporators sometimes corrode from compost residing in the underdash "box". Gas/oil with dye will usually show leaks in a day or so.

Pressostats are not PSA-specific; they are basically rated for the three pressures so should be a lot of intechangeability there.

Is this an R134A car, or an R12 one that's being filled with the later gas and has not been kitted appropriately?

boeingmech · Post by **boeingmech** » 28 Jul 2011, 22:08

the pressure switch is on the side of the condensor (off side) there is no need to evacuate the system as it sits on a shrader valve,just unscrew it. ( it is a bit of a fiddle)

i had one pack up and it was the wires goiing into it that had corroded and fell out