I looked for an answer/troubleshooting guide for this in the FSM, but didn't find anything. I notice that when I switch my A/C on that the idle speed does NOT jump up to 900 rpm as specified in the FSM, but instead drops by ~100 rpm from standard idle. I can hear the compressor clutch kick in and I'm definitely getting cold air out of the vents so I think there's enough R12 in there to possibly rule out a low refrigerant condition. The A/C was working great last summer -- idle speed kicked up when the compressor clutch engaged just like it should. Any A/C gurus out there who know the cause of this or can suggest a course of action for troubleshooting it?

Thanks!

Eric W.

Read this http://www.stealth316.com/2-isc-iac.htm

Russ <img src="/forums/images/graemlins/kewl.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" />

Thanks for the link, Russ. Very interesting reading. The ECU has to take some input signal though in order to bump the ISC up to compensate for the increased load from the compressor, right? What is it that signals the ECU? Or am I missing something obvious here?

Eric W.

Generally, it is not the input signal that fails, it is the ISC motor that fails. You turn on the AC, the ECU tells the ISC to bump up the Idle speed and the idle speed does not bump up, because the ISC is broken.

Your idle speed drops when you turn on the AC because of the extra load on the engine.

Interesting. Thanks Winston! I suppose that might also explain the issue I posted about some weeks ago where coming off deceleration with the lights on the rpms drop down to about 400 then bump back up to ~700.

Eric W.