Q: No heat after replacing dead alternator

asked by on

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.

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 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. No heat after replacing dead alternator

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: 1994 GMC Sonoma not getting power to fuel pump

The problem is somewhere in the fuel pump relay control circuit. There are five relay terminals: battery power, ignition power (controlled by the ECM), ground, output to the pump and connection to the fuel pump prime connector. What the prime...

Q: How do I use the Battery Voltage setting?

The driver information center (DIC) has a lot of information that can be displayed. You can choose what information you would like the DIC to show at any one moment. When in the Battery Voltage setting, the DIC will display...

Q: Does a bad torque converter cause the transmission to not engage into any gear at all?

What you are describing may be a result of a faulty speed sensor, potentially low transmission fluid or a even a faulty transmission control solenoid. As your vehicle travels down the road, the computer analyzes data being sent by vehicle...

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 to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
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.