Troubleshooting dead AC: Rpm INCREASE when button is pushed in... Huh?

[Bmachine]

My AC was converted to R134 6 months ago. At first everything worked great. Then I did not need to use it for a while. But now that we have a heat wave in I need it bad... and I get no cool air at all.

I did a lot of searching on this board and, based on what I have read so far it seems likely that I have a leak somewhere. But before I bring it to a specialist, I noticed something intriguing and I wondered if it might be a hint:

- When I turn the contact on and stop just before starting the engine and I press the AC button, I hear the AC fan turn on.
- I checked all the fuses and they are all good
- I do hear a relay switch on when I listen close to the fuse box. Although it seems pretty faint.
- But when I start the engine and then press the AC button, the RPM INCREASE by about 100 rpm. This seems puzzling to me. Normally when you turn the AC on, you expect the rpm to go down, not up.

Does that ring a bell to anyone?

Thanks for any help.

Bo

[jlevie]

A signal from the compressor clutch circuit tells the DME to increase idle speed when the clutch is engaged. Ordinarily that speed increase isn't noticeable due to the load of the compressor. But if the refrigerant has leaked out and the low pressure switch is open the compressor clutch can't engage and thus there's no load on the engine making the idle speed adjustment noticeable.

[Bmachine]

Thank you Jim. That makes perfect sense. Seems to confirm the leak hypothesis.

This car sat unused in a California driveway for 12 years so I wouldn't be surprised if some of the seals were hardened or even cracked.

Thank you

Bo

[jalopi]

This car sat unused in a California driveway for 12 years so I wouldn't be surprised if some of the seals were hardened or even cracked.

Pretty sure you're supposed to replace all the seals when you do a r134a conversion... I believe the issue is that r134a uses PAG oil (to lube the compressor - the lube is actually constantly circulating with the refrigerant) and that r12 systems used mineral oil. I believe the new PAG oil eats away at the r12 seals... although I could be wrong.

Regardless though, I'm pretty sure there are compatibility issues with the old seals when you convert to 134.

[D J]

Mine does this same exact thing

[Bmachine]

Thanks Jalopi.

DJ, does yours blow cold then?

[Bmachine]

As a way of testing if it is simply that the R134 has evaporated, I bought one of those Artic Freeze refill cans. Before filling it in, I took another peak inside the engine bay. And I noticed that I don't hear the compressor engage when someone presses on the blue AC switch. The auxiliary fan does come on but I hear and see nothing from the compressor. could that be bc the coolant is all gone or does that indicate that the problem might be with the compressor and not the coolant?

Thanks for any help.

Bo