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When I'm driving on cool days (Western NY) I turn the heater on and the temp ramps up from a normal 195 deg to 200-205 deg. Why is that? I would think the heater core acts as an additional radiator thereby keeping the temp at least at 195 or even a few degrees cooler. Maybe a GM engineer or somebody can explain this.
Dave
 

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AC compressor runs when ever the ventilation is set for recirculation

When I'm driving on cool days (Western NY) I turn the heater on and the temp ramps up from a normal 195 deg to 200-205 deg. Why is that? I would think the heater core acts as an additional radiator thereby keeping the temp at least at 195 or even a few degrees cooler. Maybe a GM engineer or somebody can explain this.
Dave
If recirculation is turned on, then to avoid condensation in the cabin, the air conditioner compressor is engauged to dry the air, even if the AC is not explicitly selected for ON, and regardless of the position of the temperature control.

Try this at idle. Start with the ventilation system turned off. Turn on the ventilation system as you normally would. If you hear the AC compressor engauge and make an additional wirring noise with the engine running, that's your result. Then, switch off the recirculation. After a short while (might be as long as a couple of minutes, or as short as a few seconds), the AC compressor should shut off, the clutch will be released, and it will spin down.

The extra heat plume comming from the air conditioner condenser in front of the radiator will raise the temperature of the air flowing over the radiator enough to cause this elevation in temperature.

The normal operating temperatures for this engine are well above the 195 degree minimum of the thermostat, so I wouldn't worry about it. In point of fact, the fan doesn't turn on until about 216 degrees....
 
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