TPRJIM

Hello! New guy here. Our 2004 EX has a heat problem. It comes and goes;mostly goes. I've checked the underhood cable and bled the system. I tried the diagnostic but it doesn't work as it should. The recirc light goes off and the fan blasts away for a few seconds and then nothing-only the defrost light stays on. The coldest days are gone(I hope) but it would be nice to warm up a bit.
P.S.: heat seems to come on best at highway speeds and work least around town. TIA!

GolNat

iTrader: (7)

Loosing heat at idle could be a few things. When this happened to me it was because of low coolant level. The thermostat could be stuck open, or a problem with the water pump.

How was your coolant level now? When was a water pump replaced? Thermostat?

We you drained the system did you get all the bubbles out? Air could have also entered the system through a leaking head gasket

TPRJIM

New thermostat,new coolant,pump 25,000 miles ago,bled system. I was hoping for a cheap solution before I replace the heat control unit in the dash. Thanks for your reply.

ezone

Are you talking about the fan quits abruptly?
Or something else?

Use a voltmeter or a test light at the fan motor plug to see if it lost power or ground, then test in the appropriate direction from there.

Or use your hand and beat under the dash (on the fan motor) when the fan quits. If it starts running again, the motor is bad.





If you mean you lose heat at idle but the fan still works fine, that's a completely different problem.

TPRJIM

The fan is fine.I meant that when I attempt the diagnostic the fan surges on for a few seconds and then stops. The diagnostic then goes no farther. The recirc light goes off/the defrost light stays on and nothing more happens;no problem code,etc. The heat is intermittent;it will put out heat on occasion and then drop back to cold.The AC will not give warm air which made me think that it could be the rheostat on the heat control unit.

ezone

AC is supposed to make the air cold, no?

Fan blows continuously, therefore not a fan problem....
2 theories, one is much more likely than the other...

Observe how it acts, observe what you can see:
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IF your intermittent heat follows this pattern:
"Heat is hot while driving but cools off at stops and idle....."

My nickel bet says the coolant level is low because the head gasket is blown.
(If there are no other external leaks such as hoses or water pump.)

Loses heat because the heater core has air trapped in it. Coolant may be low in the radiator, the overflow reservoir is way too full or has puked all over the right front area from overflowing.

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IF your intermittent heat loss does NOT follow that pattern above:
The other possible cause would be that the blend door actuator is moving on its own, and you should be able to observe the position of the heater core water shutoff valve in the engine compartment to verify whether this may be the case or not.
The cable for the water valve is mechanically linked to the blend door mechanism/linkage, so if it is open the actuator must be in the heat position, and if it is closed the actuator must be in the cold position.

Open the hood and check out its position when the heat works, compare to when the heat doesn't.

HTH