So my heater only works well with the a/c switched to max. If on defrost or vent it's only mildly warm. What should I be looking at/replacing/repairing. I burped my heater core and have zero bubbles in the system. I'm thinking it's the vent soleniod but am not sure. Where are the parts located at and what do I need to do to test/clean them.

Thanks

Hywel

88 formula 3.4 swap/7730 w/dis

All I can say to help guide you in the right direction, is that with the HVAC on "MAX A/C" the air is being drawn in from the interior of the car where as all other options draw air in from the exterior of the car.

I'm thinking that if either your coolant temp is LOW and not getting HOT or your heater core is dirty and not transferring heat very well the heaters performance will be poor. so if the interior of the car is at all warmer than it is outside ambient air temp than the heat will work better.

I'd verify that the Coolant temp is up around 180-210deg F and if it is consider flushing the coolant system. You can use a non contact Infrared temp gun to check the temps of the Thermostat housing, Radiator and before you get it tore too far apart the heater core. If the heater core is noticeably cooler than the radiator than it's most likely dirty inside.

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1986 SE 3800SC/4t65eHD (12.871@104.96) I'll Sell it if you like
1985 GT 3800SC (swap in progress)

quote Originally posted by 1fast2m4: ....with the HVAC on "MAX A/C" the air is being drawn in from the interior of the car where as all other options draw air in from the exterior of the car... so if the interior of the car is at all warmer than it is outside ambient air temp than the heat will work better.

I was thinking the same thing.

quote Originally posted by 1fast2m4: I'm thinking that if either your coolant temp is LOW and not getting HOT or your heater core is dirty and not transferring heat very well the heaters performance will be poor.

...or the flapper valve that controls the ratio of hot to cold air being fed through the system is not allowing enough heated air to pass, due to being either misadjusted or stuck.

When's the last time you checked inside your heater box for debris? Ever? Have a look HERE.

[This message has been edited by Patrick (edited 12-07-2013).]

Patrick, that is what I'm thinking. I just replaced my fan resistor and it was just dusty. I think I'll pull the fan and have a looksie. How do you adjust the cable?

quote Originally posted by hiwil88formula: How do you adjust the cable?

I don't even know for sure if it is adjustable. Can you tell if the flapper valve is indeed moving when you move the Cold-Hot lever?

Is your coolant system properly heating up as 1fast2m4 was wondering about? Do the rad hoses get good and HOT? If so, do the smaller hoses that go to the heater core get HOT as well?

I checked the temperatures at both rad caps and they are hot about 175 on my temp reader. I also checked both tubes on the heater core and they are hot as well. I pulled the fan and looked for obstructions and there was none, the heater core was just a little dusty. any other things i can check?