AC and RPM

[Nick Triesch]

Hi. I just did a service on my 85 911’s AC and it works! But I thought I read on this forum that when you switch on the AC, a device raises the RPM’s. I notice that when I turn on my AC the RPM’s come down a bit. If there is a device that raises the tac could you please tell me where it is ? Cannot find much info on it, Thanks, nick

[Chuck.H]

Hi Nick -

There is no 'device'... Pin 29 on the DME tells the computer that the A/C compressor clutch is engaged... it doesn't seem to raise the idle on my '89, but I think it adjusts the fuel/spark at idle for the extra load. Can you check the DME is getting this signal?

hope this helps,
Chuck.H
'89 M491 Targa, 440k miles

[86 911 Targa]

Originally Posted by Chuck.H

Hi Nick -

There is no 'device'... Pin 29 on the DME tells the computer that the A/C compressor clutch is engaged... it doesn't seem to raise the idle on my '89, but I think it adjusts the fuel/spark at idle for the extra load. Can you check the DME is getting this signal?

hope this helps,
Chuck.H
'89 M491 Targa, 440k miles

Correct.

However, there is a DME mod that will accommodate the
AC with increased RPM's.

Ingo Schmitz or Sal.carseller, both on this forum can advise.

Best,

Gerry