No Heat but the A/C works

Maintenance/Repairs
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1

I have a 1992 Mazda 929 in which the heat does not work while the a/c does work perfectly. When the problem first occurred the fusible link for the A/C was broken (indicative of some electrical overload). I replace the fusible link and still no heat.

I went under the passenger side of the dash and changed every visible black box (fuse/sensors)that is attached to the heater core unit. After that the heat still did not work.

In relation to this problem the care now runs hot whenever I am a red light or in stop and go traffic.

This seems to me a that a mechanical gate from the engine is not opening to allow the hot fluid from the engine to get into the heater core.

I have searched all resources to get a sense of what valve/gate is not opening.

Please help, it is winter time and I need the heat in this car really, really bad.

2

Blows cold air?
Try changing the thermostat if it’s over 5 years old.

3

The production of cooled air by the A/C system and hot air by the engine are two completely unrelated things. The only thing they share is the duct work inside of the car. I’d say you might worry about the blend door in the duct work, but you also said the car is running hot. So…

You are having a problem with your cooling system. (Not the A/C - the one that cools the engine via coolant/antifreeze). Get it checked out now before you wreck the engine. Step one is not to drive it again until you’ve checked the coolant level in the radiator and overflow. (Don’t ever remove a cap from a hot radiator).