Skip the auto shop - Our mechanics make house calls

Q: What Can Cause a Car Heater or an AC to Stop Working?

asked by on

What can cause a car heater or an AC to stop working?

A: There are several parts to both the heating...

There are several parts to both the heating and AC system referred to as the HVAC (heating ventilation and air conditioning system) in your automobile. Each unit has a liquid or medium to transport heat, a fan to blow the cool or hot air into the passenger compartment, and a fan or fans and cooling units under the hood. Both use some sort of power or mechanical unit to circulate the fluids. Both systems are sealed systems. So the problem can be as simple as a blown or open fuse, defective blower motor, low refrigerant level in the AC system, just to name a few.

Typically, when considering an AC system that stopped working, we are more likely to be looking at a failure to control the temperature or have air circulate in the passenger compartment. A short in the fan circuit will effectively stop the operation of each of these systems. A defective AC compressor, low system charge, system overcharge or electrical failure of the control head, or in some cases with automatic temperature control (ATC) or the electronic control unit (ECU).

Additionally, defective cooling fans, a clogged condenser or evaporator, or even a restricted H valve or orifice can cause the AC to malfunction. Loss of the ability to cool the condenser under the hood at a stop due to a defective fan can make the system appear to stop as it seems the AC blows cold when moving but goes warm when stopping.

The main issue is to properly isolate whether the system is underperforming, or it stopped all together. When it comes to the heating system, low coolant level, especially due to a leak, can be the cause. Poor performance due to a bad thermostat or defective water pump can also be interpreted as the system stopping. In either case a stuck or malfunctioning mode door or heater control valve could be to blame as well. Lets not forget a slipping drive belt as a possible cause also.

So the critical factor here is the correct diagnosis of whether it is a poor performance of the system, or a total failure of operation. Even a blocked cabin air filter can restrict the flow of air and make it appear that the AC or heater system has failed. Over time this may also lead to a failure of the blower motor, which can then need to be replaced. The key here as i mentioned is to have the HVAC system properly diagnosed to get a quick and cost effective correction.

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: A/C blows only warm air on driver's side; passenger side is cold

Some A/C systems have problems disconnecting or losing communication between the A/C control head and the temperature blend door actuators. This may require the A/C control head to be reprogrammed by a factory level scanner capable of the reprogramming of...

Q: Just had timing chain replaced on 2012 qx56 and they called" -- dealer called and said while fixing the timing belt that my ac pum

Hi there. It does seem kind of suspicious that your vehicle went in with ac and now it doesn't work. I completely understand how you feel and hope to help you fix this. However, component failure can happen at any...

Q: I noticed a smell through the heating system

Hello. It may be possible that you are leaking coolant somewhere. Most likely, the leak is coming from the intake or somewhere else near the top of the engine. Since the year of your truck is 2015, it is...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
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.