Heater core in/out???

[cederholm]

Hey guys,

My front heater isn't producing the heat that use to (hardly any in fact) on my '03. I've cleaned the sensor and confirmed the hose is attached, no change. Now I want to check for blockage in the heater core as well as replace the "T's of death".

Can someone tell me of the two hoses going to the heater core, which is the inlet and which the outlet? ...and is there a heater control valve in there somewhere? I've read many posts on the subject but no one has mentioned one.

Thanks!!

~ Carl

 

[APKhaos]

There's no heater control valve. The heater core is constantly flowing hot coolant. The air mixer doors take care of delivering air at the right temp. The T closest to the fender is the one I've always treated as inlet, but that could be wrong.

FWIW, any air in the coolant system is going to find its way up to the heater core and potentially get trapped there. I struggled with weak heat in mine until finally flushing air out of the core.

 

[cederholm]

There's no heater control valve. The heater core is constantly flowing hot coolant. The air mixer doors take care of delivering air at the right temp. The T closest to the fender is the one I've always treated as inlet, but that could be wrong.

FWIW, any air in the coolant system is going to find its way up to the heater core and potentially get trapped there. I struggled with weak heat in mine until finally flushing air out of the core.

Very helpful, thnx. What procedure did you use to flush the air out?

 

[APKhaos]

Very helpful, thnx. What procedure did you use to flush the air out?

Nothing too scientific. Disconnected both tees, put a simple on/off valve on the outlet side, then flushed hard with a garden hose thinking it may be blocked. It wasn't, but it burped up a good bolus of air. Then clamp the hoses on the core side with vicegrips [not super tight] to keep air out while reconnecting the tees. There's going to be some small volume of air introduced when connecting the tees, but not enough to be a problem.
Keep your coolant levels up to prevent this happening again.
FWIW, my problems started after replacing the radiator. Must have left some air in the coolant circuit.

 

[cederholm]

Perfect! Thanks.

 

[AimCOtaco]

I would also suggest checking the air mixer/flow control parts to make sure air is flowing across the core, seems to me the flappers are vacuum actuated and a small leak could do this. I would eliminate all the rest before pulling the core. Post up what you find, I don't remember seeing too many other threads on this issue.
Good Luck.

 

[cederholm]

I would also suggest checking the air mixer/flow control parts to make sure air is flowing across the core, seems to me the flappers are vacuum actuated and a small leak could do this. I would eliminate all the rest before pulling the core. Post up what you find, I don't remember seeing too many other threads on this issue.
Good Luck.

Thanks! Do you know of any diagrams that I can reference to find that vacuum line?

 

[AimCOtaco]

I do not but the FSM will if you can find the right one.

I just wanted to suggest that you look there before going to all the trouble of pulling the core.

 

[cederholm]

I do not but the FSM will if you can find the right one.

I just wanted to suggest that you look there before going to all the trouble of pulling the core.

Got it. Thanks!

 

[APKhaos]

Thanks! Do you know of any diagrams that I can reference to find that vacuum line?

The air mixer doors are driven by an electric motor and a tricky set of cams and arms. If you get your head down on the pass foot well floor and look up under the console you will see the mixer controller at work. With ignition on, reach up and move the temp and air direction controls and you'll see the mixer at work.

 

[2001LC]

I assume since you specified front heater you have a rear and it is getting much hotter than front?

IF NOT, the first place I'd check when heater not blowing hot enough: 1) coolant level 2) thermostat.

 

[APKhaos]

My rear heater delivered lots of heat even when the front was barely warm. Seems that the front core being mounted high makes it the place that all the random air hangs out.

 

[Somebodyelse5]

My rear heater delivered lots of heat even when the front was barely warm. Seems that the front core being mounted high makes it the place that all the random air hangs out.

Did you ever get this solved?

I assume since you specified front heater you have a rear and it is getting much hotter than front?

IF NOT, the first place I'd check when heater not blowing hot enough: 1) coolant level 2) thermostat.

Neither my front nor my rear blow hot, my coolant level was right and it's a new thermostat. I am going to try backflushing the core and see if that helps at all