Skip the auto shop - Our mechanics make house calls

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: A car that old is not going to have self di...

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 1000 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!

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: Does using heat burn extra fuel?

Hey there. The heater in the car only requires the use of the heater blower to blow hot air out of the heater case. The heat is generated by blowing hot air across the heater core inside the A/C blower...

Q: How do you adjust the second row of seats?

Your car has at least two rows of seats (some models have an optional third row as well). The second row of seats offers some of the same adjustability as the front row. Here’s how to adjust them to get...

Q: Shortage in wire leading to battery cable

Hello. If someone has changed the wiring from its original path without using the proper wires or connectors, it could cause a short. The wiring needs to be checked for any breaks or loose connections in order to make an...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.
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.