# Heat 'em up

I have two friends. Yes, that’s right, exactly two friends. Not one, not three, and 4 is right out. When I drive them to work on brisk winter mornings, my friends, Tom and Harry, turn up the thermostat in my relatively new GM vehicle with dual climate control in order for it to get warmer faster.

I notice it after I drop them off and start to feel like a foot long in Nathan’s steamer.

Let’s suppose that we are all happy when the temp is 70 degrees in the car. Is it realistic to expect that it will hit an ambient temp of 70 faster if I have the thermostat set at 80 than it would if I kept the thermostat at 70? It certainly doesn’t seem logical to me.

So, are Tom and Harry right, or can I let them know what mental midgets they are?

Call me Dick

The air that comes out of the vents is the same temp. if the thermostat is set to 70[sup]o[/sup] or 80[sup]o[/sup].

get a thermometer and take measurements, shouldnt be that hard.
in my car if I crank up the temp it most certainly pumps out hotter air but mines not so fancy.

Depending on the car, it can certainly help heat the cabin faster. If it can help, it works like this: If the water coolant temp is, say, 100 degrees, cool air is mixed with the hot air to get it down to your thermostat’s target temp of 70. If you set it to 80, less cool air is mixed with the hot.

Can you call them mental midgets? Maybe.
First off it would be helpful to know just what the ambient temp is in the car and outside the car when you pick them up. Yes it makes a difference.
Anyway in lieu of that, let me describe how our dual climate systems work (Not GM, but I suspect that their’s operate in a similar manner)
In general the greater the difference between the set temp and the actual temp inside the car, the higher the temp setting (assuming a cold car) and the higher the fan speed. As the temp inside the car starts to approach the set temp, the fan will start to slow down, and the temp flaps will move to provide a steady stream of air that will maintain the set temp.
Override conditons:
[ul]
[li]If the engine is stone cold, the car interior is cold, and the outside temp is cold, no fan until the water temp reaches a min. value (20C IIRC) then the fan speed will ramp up slowly as the coolant continues to increase in temp.[/li][li]Outside air temp will determine air distribution, cold <20C = floor/defrost[/li][li]If outside temp is >20C air is directed to face level. On some systems the change is gradual, others it is a switchover at 20C[/li][li]If defrost is selected, full fan speed is commanded, A/C compresor is switched on*, NO recirculation[/li][li]If the driver’s temp knob is moved to full hot, or full cold max fan speed is selected[/li][li]If the wipers are turned on, a bleed of air is directed to the windshield regardless of the other flap settings.[/li][/ul]
So if the guys are hopping into the car when you start it up, and flip the heat knob to full hot with a cold engine, they are not doing much except maybe blowing cold air into the cabin. The coolant has to get warm before the car can warm up. If anything running a high fan speed will slightly delay the warm up of the engine as more heat is being diverted from the heater core, that would normally be sent back into the engine. (This is a real nit pick, but hey this whole thread is kinda that way. )
If however the colant were warm, (blockheater) but the car cold, kicking the heat control to a higher temp will keep the fan at a higher speed longer, and will decrease the time to temp by a few seconds or maybe a minute. However from watching people do this time after time I am convinced that the major benefit of moving the control knob is psychological rather than practical.

I know it’s not summer, but I just want to add, that hopping into a car that has been parked in the sun, starting it and moving the knob to full cold does not do a damn thing. Since:
[ul]
[li]The system is can only produce air of about 41-44F no matter what you do with the knob[/li][li]The fan will be running at full atomic power due to the very hot air inside the car[/li][li]Recirculation has already been selected automatically[/li][/ul]

• In cold temps the compressor may not come on due to a lack of pressure inside the system, but it is still commanded on in case it will.