Pulled my daughter 91 RS 305 TBI car out of storage yesterday. It's been largely sitting in hibernation for the past 3 months while she studied in Florence, Italy.

I hadn't started the car in about a month and since the last time I started it, it has rained a lot. It fired right up and quickly found an idle. I leaks a little so I wiped down the interior of any moisture and decided to let the car run for a little while while with the defroster on. After about 15 minutes the car started surging. it would go from idle up an additional 1000 to 1500 RPM then drop back down then back up on about a 2.5 to 3 second cycle. The moment I moved the **** on teh climate control to off or to the heater the surging stopped completely and the car idled perfectly. On A/C or defrost the surging returned.

Any ideas. Could this be a bad voltage regulator? Could moisture somewhere be a culprit? Any ideas?

Thanks.

 

The AC system is low in refrigerant. The compressor is cycling on and off and causing what's happening. It is engaged when defrost is on . Either top up, or until you do, you could unplug the compressor to revert to old style defrost.

 

That's a new one. Never heard of low refrigerant causing a surging problem. I figured the issue was in some way tied to the compressor kicking on then kicking off but thought that the cars ability for the additional electrical load of running the compressor was the problem. What if the AC still blows cold air? I've got a 95' Firebird I DD that has no refrigerant also (did an engine swap back in Sept.) and I don't have this problem.

 

It just sounded kinda like what mine did. When you first turn on AC, the idle is normally increased, but would drop if the compressor cycled off, I thought that's what you were describing. Apologize if I was mistaken. Could be blowing cold from low ambient temps, and maybe the other compressor was unplugged. You could always do that?

 

Ok if the system is empty it will not do it. When it is cold or low the pressure switch reads the pressure then turns the clutch on then turns it off at a certain pressure. that is why its doing it. when it is empty, it will not engage at all. that is deffinately the problem. Unplug the connector on the front of the compressor next to the clutch tuck it back behind the compressor until summertime and forget about it.

 

That it was I was trying to describe. With the AC or defroster on after running for 15 minutes with the car idling smoothly with no change in RPM the engine began surging on it's own as the compressor kicked on and off. Normally these additional draws on power are compensated for by what I thought is the voltage regulator to keep the rpm's constant but each time the compressor kicks on and off the RPMS's jump and drop. The AC deos blow cold or rather cool and the refrigerant could be gone for all I know. I haven't checked it yet. I just nerver heard of low refrigerant causing a surge before. Again my dd Firebird has no refrigerant and never surges.

I'll try unplugging the compressor and see what happens, but shouldn't the clutch kicking on and off not impact the RPM's? When it kicks on under proper conditions if say there is refrigerant the RPM's don't rise and fall with the compressor coming on and off.

 

With the a/c on the idle is supposed to kick up. because more strain is being put onto the belt and engine.