Question about GMC Envoy
The "Tachometer" is the gauge that indicates the engine RPM. It is not unusual for the idling RPM to drop slightly when the air conditioner comes on. The air conditioner represents a fairly large load on the engine so when it starts, the RPM will drop slightly. When driving, you'll probably not even notice that the air conditioning is a load on the engine unless you're accelerating uphill, pulling a trailer or passing another vehicle while the vehicle is fully loaded. At idle, the Envoy's computer should detect the falling RPM and make adjustments in fuel delivery to bring the RPM back up.
In any case, it shouldn't be cause for alarm, unless the air conditioner is stalling the engine. If this is the case, you are probably in need of service. The issue of low cooling from the air conditioner while idling in gear (as is the case when stopped in traffic, etc.) is correctable free of charge at the dealership on certain vehicles as a result of a recall. Your dealer can tell you if your vehicle is affected or if there is other recall work pending on your vehicle based on the VIN.
I hope this helps!
Posted on Nov 04, 2009
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