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

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Heating works only on defrost and works only at high speed

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: No heat

This may be due to a faulty heater blower motor or potentially a bad heater core. As you may know, the heater core is a small radiator like unit that circulates the hot coolant from the engine through the heater...

Q: Car idle is erratic and exhaust gas smells strange.

Hi There! It sounds like you may have a dirty or failing idle air control valve causing your engine idle to fluctuate and eventually stall. In the mornings it is normal for the engine idle to be a bit higher...

Q: Throttle body problems

Hello. You need to hold the throttle body open and put the cleaner on a rag and rub inside the throttle body top and bottom where plate contacts and then clean the edges of the throttle plate. If after cleaning...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.