Is the a heater core problem?

[edwardr]

Hi forum,

This is my first post. I need your help to diagnose a problem. My car is a 1990, 3SFE.

When I turn on the heater, my windows fog up. No amount of heat will get rid of it. When I turn on the A/C with the temp. slider still set to heat, the fog clears up.

I suspect that extra humidity is coming from a leak in the heater core but I haven't found any dampness anywhere to confirm this.

Has anyone had similar symptoms and found the cause of the problem? I don't want to tear into the dash to replace the heater core unless I'm pretty sure that's the problem.

I appreciate any and all advice.

[toyomoho]

Is this a new problem, did the heater ever defog the windows in the past? Is the heater control on outside air (best) or recycle? When the heater control is on defog, does hot air actually come out of the upper dash vents to defog the windows?

The A/C defogs the windows a lot faster, this is normal. Running the A/C to defog windows is fine and will not hurt anything.

Before you take the car apart, start keeping close tabs on the coolant level. If staying the same, you do not have a leak. If a leak, you may also smell coolant in the car.

[fredk]

does it smell like anti freeze?

[da_horse]

get a coolant system pressure test done.that will let you know if there is an issue with your heater core or not. but your symptoms sound similar to what i had when mine went.

[Doctor J]

At the time when you turn the heater on is air mixer is on FRESH or RECIRC position?
High humidity inside the car such from the damp carpet or plugged up heater/a/c unit drain tube are addding extra moisture to the inside air.