Skip the auto shop - Our mechanics make house calls

Q: While driving defroster set to hot blows hot air as it should, while idling it is blowing cold air.

asked by on

While driving defroster set to hot blows hot air as it should, while idling it is blowing cold air. When I stop at a light the air almost immediately becomes colder, as I accelerate the air begins to get warmer, seems to take longer to switch from cold to hot than it does to switch from hot to cold. There is no change in fan speed. The car never did this before.

My car has 108000 miles.
My car has a manual transmission.

First, the coolant level should be checked to make sure the radiator is full. While the overflow tank may be full, the radiator cap must be taken off to check the level inside the radiator. If you find the level is very low, you have a coolant leak that must be fixed. If coolant levels are normal, an engine thermostat or heater control problem may be what you’re experiencing. Consider hiring an experienced technician like one from YourMechanic who can come out and take a closer look at your lack of heat concern to offer a more personal diagnosis.

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!
  1. Home
  2. Questions
  3. While driving defroster set to hot blows hot air as it should, while idling it is blowing cold air.

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: fan won't work on first setting

Hello. When the fan motor is not working on a specific speed, it's most commonly due to a problem with the blower motor fan resistor. The resistor’s job is to send the proper voltage to the blower motor fan for...

Q: 42rle transmission driveshaft have different part numbers.

The best thing to do is cross reference the part number with the dealership and the parts store. Keep in mind, the part number on your jeep is from the dealership and not a local parts store. So if you...

Q: replaced ac relay and recharged ac which worked for a few days. Also can hear clicking from actuator in glove box. Any suggestions

If the A/C system was working properly (producing cold output) and then just "suddenly" stopped, broadly there are two possibilities: 1) you have a leak and consequently the refrigerant level is too low; or 2) the refrigerant charge is undisturbed...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
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.