Q: Heating works only on defrost and works only at high speed

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Hey Everyone,

I bought an old Toyota Corolla and there are some issues with the heating and cooling I'd like to try and fix. I just put a relay in that enabled the defroster to work. Currently, the only air things that work are defrost at full-speed, or I can completely turn it off. If I completely turn it off, the machine makes a noise that is a constant, slightly high pitched tone. The only other part of the air that I can control is the temperature. So it goes full-tilt defrost, no defrost with a constant noise, or I can change the temp.

1) I would like to be able to stop the noise when I turn off the defrost. 2) I would also like to be able to direct the air to other portals, but I understand that might be harder.

This car was owned by two mechanics previously. No engine or tranny problems. Has about ~300,000 miles. The radiator and water pump were replaced about a year ago.

How do I go about seeing what is wrong? A code reader? Thank you!

My car has 300000 miles.
My car has a manual transmission.

A car that old is not going to have self diagnostics in the heat AC system. So you don’t need to bother with checking codes. Most cars use engine vacuum to control the heater flaps, and the defrost is the default position, so first you need to check all the vacuum hoses under the hood. find a vacuum diagram and check every hose. One vacuum line could make a big difference. As for the fan speeds, you probably need a blower resistor. High speed comes through the relay, all the other speeds come through the resistor. The high pitched squeal might be the fan motor itself. All this and more could be easily addressed by contacting your mechanic. They can send a technician to your home or office to check out your climate control and make recommendations as to what you should do next.

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