Climate control blows hot air while driving, cold when stopped.

[Crazy_pilot]

In keeping with the trend of climate control questions...

My car has always done this, I've just never bothered to post anything. When the engine is warm and I'm cruising, it blows hot air just fine. But when I slow down and stop at a light it starts blowing cold air. Anybody have a similar thing with their car? I've mentioned it to a few friends, one of which suggested a failing water pump, but this has been happening for the two winters I've had the car, and the temp needle has never climbed above the little squiggly lines of the water temp logo, not even halfway on the gauge, even in extended idling during hot weather.

My only theory is that I may have a partially blocked heater core, and/or there isn't sufficient coolant flow at idle (less than 600 RPM in my car) to bring any heat in.

Any thoughts?

[1986nate]

If it was only in the winter that it did this I would possibly think the thermostat but since its the same way in summer I don't know.
If it was a partially blocked heater core it would probably cause the car to overheat in summer driving/idling unless it were to bypass the heater core when the heat is off???

[redlightningsvx]

Mine doesn't do it so I would say blockage because when your moving it's forcing the air and when stopped it's not.

[Crazy_pilot]

It's only in the winter. If it was the thermostat I would expect to see it on the gauge, either never warming up because it's open all the time, or spiking and then dropping because it's sticking closed until the pressure forces it open. That was the behavior I saw in my Taurus before I changed the t-stat.

[1986nate]

It could be the Air door inside the HVAC that controls whether it allows outside air in or not- that its not closing out the outside air all the way when in heat mode...

[1986nate]

Otherwise make sure that the coolant level is full where it should be but I'm guessing you have checked that over the time of ownership and the few years of having this problem. If none of those than likely it is your water pump getting "tired". Odd that it would last this long though...

[Crazy_pilot]

Originally Posted by 1986nate

It could be the Air door inside the HVAC that controls whether it allows outside air in or not- that its not closing out the outside air all the way when in heat mode...

Hmmmm...That's something to look into. That would be the flap above the blower motor, correct?

[1986nate]

Originally Posted by Crazy_pilot

Hmmmm...That's something to look into. That would be the flap above the blower motor, correct?

Not sure about location. I was just throwing out possible solutions to give ideas.

[Crazy_pilot]

Alright, thanks. I'll pull some things and check that out more thuroughly when I've got some free time. It's not a problem so much as a small annoyance. My drive to school is only 10 minutes, so not really a big deal.

[1986nate]

Originally Posted by Crazy_pilot

Alright, thanks. I'll pull some things and check that out more thuroughly when I've got some free time. It's not a problem so much as a small annoyance. My drive to school is only 10 minutes, so not really a big deal.

Still if you're like me then I'm sure if possible you want as much as possible to work properly.
And be sure to post any findings/solutions as I would like to know what the final culprit is.

[kwren]

Originally Posted by Crazy_pilot

Hmmmm...That's something to look into. That would be the flap above the blower motor, correct?

The 2 levers to control the flaps are on the other side of the unit away from the blower and easily seen (with a flash light),and accessed, by looking under the dash from the drivers side.

[Francis]

this happened to me, it had no more coolant inside rad , topped it and after it was okay ....

[Hondasucks]

Originally Posted by Crazy_pilot

Hmmmm...That's something to look into. That would be the flap above the blower motor, correct?

The flap above the blower is what controls whether the air comes from the outside of the car, or from the inside, and is controlled by the "CIRC" button on the climate control unit.

[oab_au]

Originally Posted by Crazy_pilot

In keeping with the trend of climate control questions...

My car has always done this, I've just never bothered to post anything. When the engine is warm and I'm cruising, it blows hot air just fine. But when I slow down and stop at a light it starts blowing cold air. Anybody have a similar thing with their car? I've mentioned it to a few friends, one of which suggested a failing water pump, but this has been happening for the two winters I've had the car, and the temp needle has never climbed above the little squiggly lines of the water temp logo, not even halfway on the gauge, even in extended idling during hot weather.

My only theory is that I may have a partially blocked heater core, and/or there isn't sufficient coolant flow at idle (less than 600 RPM in my car) to bring any heat in.

Any thoughts?

Two points come to mind. First and foremost, is air in the system. The heater and the throttle body are the highest points in the system, so air will collect there. At low speed it will stay there.

Secondly, as you say, the rotational speed of the pump is slow. The flow through the heater is dependant on a pressure difference between the inlet and the outlet. When the engine is hot, the thermostat is open, and it is idling slow.
The pump is not rotating fast enough to produce the necessary pressure difference. This is made worst by the by-pass circuit that parallels the heater circuit. So the flow though the heater slows down and the blower fan cools it.

Harvey.

[Crazy_pilot]

Thanks Harvey, I'll put the funnel cap on the rad shortly and bleed any air out of the system. I suspect there may be, as my overflow hose isn't the best fit to the PWR rad's nipple and I've seen evidence of leakage.

I'll also check all the actuation linkages while I'm doing that, see what may not be moving.