problem with constant heat supply

Jvan · #1 01-08-2010, 07:43 PM

Now that the really cold has hit the northeast, my heat is erratic. When I'm driving the heat seems to respond to the temperature setting. But when I stop for a light or any other reason, the heat stops and the air blowing thru the system is cold. When I start to move again, the heat returns while the car is moving. I tried to clean the temp sensor on the dash but that had no effect. Any suggestions?

Crazy_pilot · #2 01-08-2010, 07:49 PM

Same problem with mine, it's been doing it for over a year now. I've bled the coolant system, changed the thermostat, changed the water pump...all to no effect. What I want to try is back flushing the heater core with CLR to clean it out. It's irritating when the temps are hitting -30 to -40 here.

Trevor · #3 01-08-2010, 10:53 PM

Here we have two members involved with the same problem.

It would appear that heat is only available when the car is moving, correct?

Does this occur in both manual or auto modes, or is it confined to auto?

It would appear that the operation of the motor driven heater air mix door must be involved, and very likely the control system of same.

In respect of control and forward motion, I wonder about the ambient sensor mounted behind the front grill. Any mods that could have an effect on this?

Gamesy · #4 01-08-2010, 11:57 PM

same issue with my 2003 RS

AyeJaye · #5 01-09-2010, 08:02 AM

My 92 does this as well. I thought it was related to my needing to switch out the radiator, but now I'm wondering...

Jvan · #6 01-09-2010, 10:16 AM

You are correct that the heat does come out the vents when the car is moving but not when it's stopped. Cold air does blow out the vents whenit's stopped so the fan is working. This happens when on auto mode but I don't understand what you mean by "manual"mode. My heater/ventalation system is controlled by the temp setting on the round gauge in the dash. Depending upon the temp setting and the sensor under the gauge, I either get heat of air conditioning . If I push the vent button, I still can add heat to the incoming air if I raise the temp setting. So please explain what you mean my "manual" mode. The car is very stock except for koni inserts and Brembro rotors. There are no mods that would effect this. The car is a 94 w/178,000+ miles and this never happened before. ???

svxcess · #7 01-09-2010, 10:51 AM

In AUTO mode, the fan speed is set based upon the temperature you set and the inside cabin temperature. The temperature setting in AUTO mode also directs where the air exits. You will notice that as you lower raise or lower the temperature setting the fan speed changes automatically as the setting comes close to the inside cabin temperature.. The AUTO led is illuminated.

High temperature settings in AUTO should come out at the floor vents. If the DEF button is pressed, hot air comes out of the windshield/side vents.

Once tou set the temperature, if you manually change the fan speed (low/med/high) it is no longer in AUTO mode (that LED should be off)

And then there is ECON, which does basically the same thing, only not automatically-controlled. In this mode the compressor does not run, so dehumidifying is not present for clearing the windshield. I use ECON for heat in the cooler weather if I don't need to keep my windows from fogging.

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Crazy_pilot · #8 01-09-2010, 11:12 AM

In my case it's dependant on engine speed. If it is held above 1500 then I get heat. If the RPM's fall below that I get cold air. The cold does not come on immediately, only after 20 seconds or so of idling. For example, my drive to school involves a 55 MPH road. If I'm cruising on it I get heat and all is well. When I see a red light well ahead of me I let off and coast. Initially the system continues to blow hot air, but after a short period of coasting the temperature falls.

It should also be noted that the cold air coming in is not as cold as the outside air, just significantly colder than it should be.

This leads me to believe that the heater core isn't getting proper circulation. When the RPM's are raised and the coolant pressure increases there is sufficient flow to heat the air flowing over the core. However, once RPM's drop so does the coolant flow. Initially there is enough hot coolant in the core to provide momentary heat, but once this has been used up by the airflow there is not sufficient heated coolant going through the core to continue providing optimal heating. Because the incoming air is never "ice cold" I believe there is always some minimal flow of coolant, just not enough at idle to heat the air properly.

Jvan · #9 01-09-2010, 11:55 AM

Now I understand what you meant by "manual". Yes, I've changed the fan speed from high to low and in between but I never realized that doing this took it off auto control. Leaned a new thing today. I haven't checked at what rpm this happens but I'll pay attention today/tomorrow. I had something similar in a Taurus that I used to own. In that case I couldn't turn the heater knob beyond the halfway point and cold outside air was entering the car all the time. After a expensive removal of the dash, I discovered the problem was a pencil that had fallen thru the defroster vent and lodged in the heater door and prevented it from fully closing. It's not a pencil this time but it is annoying and my wife would like it FIXED!!!

Trevor · #10 01-09-2010, 03:48 PM

It would appear that my JDM car has a different air conditioning and heater system from the US version. Therefore I must leave you to your own devices.

Crazy_pilot · #11 01-10-2010, 04:37 PM

Update: I filled the heater core with CLR at the shop today and let it sit for a couple hours before flushing it out and re-filling the coolant. I don't have results yet, as the car was sitting in the shop all day and was therefore pretty warmed up, plus 30 minutes of idling to bleed the coolant. I can say, however, that my right foot was much more toasty than it has ever been before. I should know for sure when I drive in tomorrow.

Crazy_pilot · #12 01-18-2010, 10:24 AM

Another update: Oddly enough for this part of the world, it's been a warm January, hovering just below the freezing mark (even above yesterday!), so I have be unable to evaluate the effectiveness of the flush so far. One of these days the temps should drop down to the typical -40, so I'll update again when I know more.

Crazy_pilot · #13 01-26-2010, 07:39 PM

Another update:

The temperature dropped back down well below freezing today. Drove the car home and didn't notice any problems with the heat supply. I was taking some of the back roads home, so it took most of my drive to get the coolant up to temp, and only got really good heat when I was a few minutes from home, but I didn't get the old cold air blowing up my ankles thing. I can't proclaim it a full fix yet, I want to drive it a bit more in my normal routine in cold temperatures, but things are looking up.

Gamesy · #14 01-27-2010, 11:10 PM

ya crazy, wait till february, apparent we're in the "january thaw" then we'll have the "february freeze" :S

Pure_Insanity8 · #15 01-28-2010, 02:04 PM

Has anybody tried replacing the thermostat? My Leggy was doing that a couple winters ago... new thermostat... problem fixed. Apparently I was only getting a small amount of coolant through, so under load and higher rpms it could force enough through for everything to work normally. I also found that the aftermarket thermostats suck... went through 2 in less than a year (the OEM one was by far superior).