I have a 2003 auto Protege 5 and it appears the
heater is on even though the fan is turned
off. I usually have the temp gauge to cool
and the air coming from the vents is cool.
I just figured it was the effect of the air
blowing in. But when I turn the dial to warm,
I can definitely feel a change in the temp
even though the fan is switched to off.
I don't think this is related to the compressor
being on (is it?). I have the vent at dash/
floor right now so that should have the comp
off, right?
I'm trying to increase MPG so any little bit
can help.

Thanks, Paul

 

do you mean the defogger is on? because then you go on to say the air coming out is cold but when you turn the temp up it is warmer. it doesn't make any sense.

if your selector is set to either of the last two settings clockwise on the dial then yes the defogger and the a/c compressor comes on. if it is on any of the other setting then the a/c compressor is not on. you probably are just feeling the air coming in from having the fresh air selected instead of recriculating air selected. your compressor coming on for your defogger will have such a small effect on your gas mileage it will probably be unnoticable.

 

The valve that controls hot water through the heater may not be closing completely. I had that problem on another car. Replacing the valve may fix it. So may beating on it with a wrench.

All my tools are hammers except my screwdrivers, which are chisels.

All three of the last positions clockwise run the compressor (floor; floor/def; def).

 

Is it set to allow air from the outside? One of the switches allows only circulation inside the car- this closes the vents to the outside. The other allows air from the outside to enter the cabin. If this is selected, air will flow in depending on the speed of the car- the faster the car the greater the air flow.

 

The air flow is coming through the front, not recirculating.
The vent is at dash/floor--compressor should be off. The fan is
off. When the temp control is at cool, the air is cool (and so
is the outside air). When the temp control is set to warm,
the air is warm (but the outside air is not). When I turn it
back to cool, the air gets cool again. So the heater must
be on even though the fan is off. Is this normal?

 

now i follow you. completely normal when you turn your temp selector to hot it has nothing to do with the fan. it opens a valve and allows hot coolant from your engine to flow through a small radiator, called a heater core, under your dash. the air being forced through the vent gets hot from going through the heater core. your fan control doesn't control anything but the fan.

 

If you don't want the air to come in through the vents (with the fan off), you need to turn the recirculate function on. Mazda's have used this design for a long time, and it confuses some newer owners from other makes.