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

asked by on November 23, 2016

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.

Heating AC Inspection $79.99 - $89.99 Get a Quote

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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

What others are asking

My gas mileage has dropped to 22 mpg, what could be the cause?

When a vehicle gets poor fuel economy, it's typically due to an electrical sensor that is faulty, such as the oxygen sensors, the air fuel ratio sensor, dirty fuel injectors, or the throttle body being dirty. Driving habits can also...

Check engine running rough

You may have overfilled your engine with oil and the excessive oil started to foul out the engine cylinders. Have the oil level sensor checked by having a mechanic diagnose the problem and Check Engine Light to see if oil...

My check engine light is on and the autozone said it's the fuel rail pressure sensor and its high. I am supposed to drive to Texas

Hi Kelly. A check engine light is typically triggered when a senor detects a mechanical or electrical failure within an engine or transmission component. It usually will be accompanied by symptoms. In the case of a fuel rail issue, the...

Car heaters blowing cold air when driving

The lack of heat being generated by your system may indicate a clogged heater core. The [heater core]((https://www.yourmechanic.com/services/heater-is-not-working-inspection) is a small radiator like unit that circulates the hot coolant from the engine through the heater core which then uses this...

Parking brake warning

Be sure the warning light pertains only to the parking brake and not, in addition, the brake fluid level. If the warning light pertains only to the parking brake system, that system has a switch that could be sticking in...

My 2002 jeep grand Cherokee keeps running hot. I replaced the water pump, thermostat, relay for fan,tempature sensor and the radia

Be sure not to drive the car if it is overheating because overheating can warp the cylinder head and/or engine block causing costly damage. The most common causes of overheating include low coolant level, a faulty thermostat, a plugged radiator,...

Weak heat in all vents, cold air comes out of drivers. 2008 Jeep Wrangler

Hi there - I believe you have a problem with the heater air blend doors. As you know, the lack of heater function could have 5 causes: the engine is not getting up to correct temperature (center of the gauge)...

Battery light stays on and overnight battery drain. 2006 Land Rover LR3

Hi there - yes, something is going on here that's draining your battery. Perhaps the pressure of the engine wash dislodged wiring which has shorted, or there was a chemical reaction to the cleaning solution that caused electrical damage in...

There is no heat blowing out of the inside vents.

No heat from the vents can be caused by a few different things. A few things I would check are the thermostat and heater control valve, as these are two components that control flow to the heater. If the thermostat...

Related articles

Signs You Need a New Car Heater
Car heaters are a key car part for those living in cooler climates. A common sign your car heater isn't working is when air doesn't heat up quickly.
The Best Used Cars to Buy for Senior Citizens
Everyone Everyone needs a way to get around. You need to get groceries, get to doctors’ appointments, visit with family and more. However, senior citizens have very different needs when it comes to buying a used car than other demographics....
Symptoms of a Bad or Failing Heater Blower Motor Resistor
Common signs include the car's heater not working or getting stuck on a certain speed, or something getting jammed in the blower motor.