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My heat doesn't work in my 98 Honda civic. I just had the radiator and the fan motor replaced. I haven't had a chance to test it will this fix the problem?

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There are a few things that can prevent heat in an automobile from working. The first step is determining if there is no heat due to lack of air flow or lack of heated coolant flow.

A note on coolant level; if it's too low, there may not be enough to flow to the heater core (a heater core is a little radiator inside the cabin of your vehicle).

You wrote that you had your radiator and fan motor replaced. It's highly unlikely that the person who filled the system didn't fill the cooling system fully. Also that generally excludes the fan motor as faulty but some parts can be bad when brand new.

When filling the coolant system, some vehicles have a requirement to purge air from the system. If there is air in the system, coolant doesn't flow as expected in those vehicles and can overheat (my Audi A4 2.0T for example).

After ensuring the coolant is at the manufacture determined level, start your vehicle and allow it time to warm to normal operating temperature (utilized your temp gauge on the dash).

Turn on the fan and adjust the temperature control to call for heat.

If the fan does not turn:

  • Check fuses
  • Check for power at the fan connector. You should have 12 volts on high speed, lower at lower speeds. If no power with a good fuse, could be a bad switch, resistor or wiring.
  • note - Often times, the fan generally has a resistor pack installed into the ventilation system. When running at lower speeds, it lowers the voltage to the fan motor via voltage drop across a resistor in series with the motor - some vehicles with electronically controlled speed will most likely operate on Pulse Wave Modulation and require an oscilloscope to diagnose.
  • Check for a bad fan with 12 volts applied using jumper wires to connect it to battery or a 12 volt power supply
  • Remove the fan and see if it spins by hand

If the fan turns but no air blows out, is the ventilation system obstructed?

  • Check for obstructed cabin air filter if equipped
  • The duct work could be disconnected inside the dash
  • It's highly unlikely but the blower assembly may be missing the vanes (if it's a used car and you have no idea what happened to it before you picked it up)

If the fan turns and air blows out but is cool

  • Check the coolant level
  • Check the valve that allows coolant to flow to the heater core
  • The heater core could be plugged
  • The cooling system may be modified and there is no coolant flowing to the heater core

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