Why does my heat stop working when I stop my car?

To fix your car's malfunctioning heating system, you first need a basic read of the situation. Is the heater blowing cold air into the car, or is the car heater not blowing any air at all?

If cold air is coming out of the heating vents even when the vehicle is warmed up and the thermostat is set to hot, you could be dealing with one of the following problems:

• Low coolant.
• A blockage in the heater core.
• A stuck blend door.
• A stuck heater valve.
• A bad switch or linkage.

If the heater isn't blowing any air, the problem is likely a faulty blower motor or electrical connection.

These instructions will help you diagnose and fix a car heating system that blows cold air. If the heater isn't blowing any air, skip to the next section.

1. Check the coolant level. Turn off the vehicle and let the engine cool completely. The coolant is housed in a translucent plastic jug in the engine compartment. It should have level indicators that show how full or empty it is. If the coolant level is low, the vehicle likely isn't circulating enough antifreeze through the heater core, and it needs to be replenished.

   Adding coolant might fix the problem in the short term. However, low coolant often indicates another problem, such as a leaking gasket or hose. If the vehicle burns coolant, it may have a blown head gasket, which can be costly to fix. Dark brown coolant indicates rust in the cooling system.

2. Check the heater core temperature. Lift the hood and check the temperature where the heater core hoses enter the heater core box. The safest way to do this is with a non-contact infrared thermometer. If one hose is the same temperature as the coolant and the other hose is cold, a blockage might exist in the heater core. If the vehicle has a valve in one of the hoses, check its operation. A stuck valve prevents coolant from flowing through the heater core.

3. Check for debris in the heater box. If you determine that hot antifreeze flows through the heater core, debris such as leaves, pine needles, and road debris might be stuck in the heater box.

4. Switch the thermostat from hot to cold and listen. If you don't hear the blend door moving, the problem might be the blend door, linkage, wiring, or the thermostat switch, depending on the vehicle.

If the heater isn't blowing any air, a faulty blower motor or electrical connection might be the problem. Follow these steps to fix it.

1. Check if the blower motor receives power. The only way to determine which component has failed is to grab some basic diagnostic tools, access the blower motor, and check whether it receives power. The specific diagnostic procedure varies with the vehicle.

2. If it receives power, check if the blower motor is burned out. After removing the blower, you might find a squirrel cage so clogged with debris that the motor can't operate. In other cases, a broken wire, rusted connections, or a disconnected pigtail assembly might be the issue.

3. If the blower doesn't receive power, check that the blower fuse isn't blown. A blown fuse often indicates an underlying problem, so never replace one with a larger fuse to prevent it from blowing out again. If you replace a blown fuse with one of the same amperage and it doesn't go out, the fuse likely failed due to age. If the original fuse is not blown, trace the problem to the source by testing the resistor, relay, and switch.

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You pull up to a stop in your car on a cold day, and suddenly your cabin's heat turns into an icy blast. What gives? Stay warm this season by learning what could be causing your heater to only work when you drive and what you can do about it.

Why Does My Car Only Blow Hot Air While Driving?

Your car's heater works in tandem with your engine's cooling system. Many issues with inconsistent heat in the cabin can stem from coolant-relatedissues. If your car only has heat when driving, the following issues may be to blame.

You May Have Low Coolant

Coolant regulates engine temperature and the flow of hot air into the cabin. Your engine accumulates a lot of heat when working, and coolant helps to collect this generated heat by transporting it to your vehicle's radiator for cooling. 

If the coolant is low and your heater is on, you may notice that your car heater only works when driving. A properly functioning coolant system is essential to many components within your vehicle, and having no heat at idle is typically a sign that something is amiss. The first thing you should check in this instance is your coolant level. 

Caution: Never open a perceived hot or pressurized cooling system. Doing so could lead to personal injury. Check your owner's manual for how to check coolant levels or have a professional check the cooling system for you.

There are many reasons for low coolant levels, including irregular maintenance and leaks within the coolant system. Whatever the cause, it's best to have the issue inspected by a professional technician at your local Firestone Complete Auto Care. 

Your Thermostat is Stuck Open 

Your vehicle's thermostat helps to maintain proper engine temperature by controlling the flow of coolant out of the engine. Debris and corrosion build-up can prevent it from closing correctly. When this component is stuck open, you may experience low engine temperature. If the engine does not warm up as it should due to a stuck open thermostat, the heater won't be able to build up the warmth needed. The result: your car's heater may stop blowing hot air — idle or otherwise.

Your Heater Core May Be Clogged

While a blocked heater core is not one of the most common car heater problems, it could ultimately be the cause. The heater core uses hot engine coolant from your car's cooling system to warm your vehicle's cabin. When this component becomes clogged, you may start to experience car heater problems.

The water pump pushes hot coolant through heater hoses to the heater core. Then, the blower motor moves air across the heater core fins, allowing warm air to blow out of the A/C ducts. In some vehicles, a valve opens up and allows hot coolant to flow to the heater core when you turn on the heat. This coolant, typically around 200 degrees, then delivers the hot air needed to your car's interior. 

Your heater core may become clogged due to debris build-up. It may also start to malfunction if the cooling system is not maintained properly. When you're dealing with heater core problems, it's best to have your vehicle inspected by a professional since this component can be difficult to access (located deep behind your dash on most cars) and messy to fix.

Your Coolant System May Be Airlocked

If your heat only works when driving, this can also be caused by air pockets. Air pockets within the cooling system can prevent adequate coolant circulation and are sometimes the result of low coolant or a faulty radiator cap. 

However, low coolant levels are often the culprit in this situation and can lead to poor engine performance, overheating, and inconsistent heat (or cold air) coming from the vents in your cabin. 

Get Heat and A/C Service at Firestone Complete Auto Care 

Don't wait till the first big frost to take care of car heater problems! If your car only has heat when driving, schedule an appointment at your nearest Firestone Complete Auto Care for professional heat and A/C services.