Q: No heat after replacing dead alternator

asked by on October 28, 2016

I had my alternator die the other day and I replaced it. During the time period my low battery and low fuel light came on and I lost my heat, after replacing the alternator my lights are still on and still no heat. I was told to check my blower motor and the relay. Do you have any suggestions on what to check? Thanks Randy

My car has 223000 miles.
My car has a manual transmission.

Heating AC Inspection $79.99 - $99.99 Get a Quote

The alternator, low battery, and fuel light will have no effect on your heat. Your lack of heat is a separate issue aside from a car that won’t run and cannot produce any heat. Someone has suggested you check the blower motor and relay indicating you don’t have any air flow out of your vents. It’s important to understand there are two scenarios here that can create a lack of heat output. There can be no air coming from the vents, or the air coming from the vents will not get hot. These are two distinctly different problems with different solutions.

If you don’t have air flow, tap on the blower motor with a small hammer while the blower is on. If it begins to work again, you need a blower motor. This is always the first step I take when a vehicle does not have air flow out the dash vents. If this doesn’t work, then it is time to consider other parts of the electrical circuit. The relay is certainly a good place to begin, as well as checking fuses and the blower motor resistor. Blower motor resistors are the most common failure items in these circuits. If all these check out good, the last thing to consider is the blower motor switch on the dash.

If you have airflow with cold air, you will first need to make sure the cooling system is full. Do this when the system is cold by removing the radiator cap. If it is low, you have a leak in the cooling system that needs to be repaired. Top it off if it is low and be sure to fill the overflow jug as well. Run the motor for awhile and keep in mind you may need to bleed air from the cooling system, if it was low, this will affect the heat output in the cab because air bubbles always seem to begin in the heater core first.

If that doesn’t fix it, you will want to feel both heater hoses, assuming the cooling system is full. Both hoses should be hot with one being slightly cooler than the other. If one is cold and the other is hot, you have a clogged heater core. If both are cold, you have an air bubble in the heater core and possible other parts of the system.

If you need further assistance getting this checked, a certified professional from YourMechanic can come to your car’s location to diagnose the heating issue and follow through with repairs.

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


Experienced Mechanic?

Earn up to $70/hr

What others are asking

DTC: P0171 and DTC:P0174

A number of things may cause code P0171 and P0174 to be triggered. As the codes indicate, this means there is a lean fuel condition which may be caused by a lack of fuel supply or in some cases, a...

I have a 2015 chevy impala, my key is stuck in ignition, car will not turn over but key goes forward and back, steering wheel is n

Hi there. When the key is stuck in the ignition cylinder, it can be caused by debris inside the cylinder, the key being slightly twisted or the cylinder being damaged itself. It is also possible that a different safety system,...

Parking brake, ABS and traction control lights are all on

Hi There, It sounds like you are correct in that the lights may be on due to one or more faulty sensors. It is hard to say how many. It only takes one of them not working properly to set...

I moved my truck and it started fine. Went to get back in it and it wouldn't start just a faint single click.

You may have a problem in your wires somewhere. If you have a wire short it could possibly cause this. However, you may have a faulty part. Look for wires around your starter that may be touching the frame. Is...

Do you think it is the starter

Hello there, thanks for your question. I believe you are correct in the fact that the starter is most likely your issue. If all the lights, windows, radio, and wipers all function properly as they should, most likely the battery...

Small bump caused rear-end suspension & stabilization bar damage

This sounds interesting. I have not experienced such a situation before. I can't imagine a small bump causing such damage unless the vehicle crossed over the object with the rear end and possibly bent something. You may want to at...

engine vibration at idle 2012 Dodge Charger

Hey there. I would recommend taking the vehicle to a local dealer to have the vehicle checked for recalls and also technical bulletins for this engine. There are cylinder head replacement and timing chain replacement recalls that may pertain to...

Ticking noise

Hello there, a few different faults can cause the vehicle to have this ticking noise. The most common faults would include an issue with the flywheel, belt tensioner, alternator, water pump, or engine mechanical issue. I'd recommend getting some help...

Parasitic drain on battery.

Hello, it sounds like you are really close to a solution since you know what is causing the draw. I would check with the relay that powers up the PCM. Locate the PCM relay in your owner's manual or fuse...

Related articles

How to Buy a Good Quality Heater Control Valve
When When your heater does not heat, it is a pretty obvious problem. What is not obvious is exactly where the problem lies. Chances are, the problem might be with a little part called a heater control valve. This essential...
Can a Car Battery Freeze?
Cold temperatures can make it hard to start your car, and extreme cold can freeze a battery. Use a battery heater to make your car reliable in winter.
Symptoms of a Bad or Failing Heater Blower Motor
If your car's heater doesn't work, only works on certain speeds, or only cold air comes out, you may need to replace the heater blower motor.