While both the heating and AC are connected - to an extent - within your car, they’re actually separate systems. Your car’s heater uses heated engine coolant to warm the air that is blown into the cabin, while the air conditioner uses a compressor driven by the engine, combined with both high pressure and low pressure lines, special refrigerant and many other components.
Potential problems with your car’s HVAC system
The potential issues here vary whether your heating has gone out or your car’s AC system is on the fritz.
Common reasons for the heating system not to work include the following:
- Low coolant
- Air in the coolant system
- Malfunctioning heater core
- Failed (or failing) thermostat
The potential issues with the AC system are different, and include:
- Low refrigerant (will generally blow cool, but not cold)
- Damaged compressor
- Damaged compressor clutch
- Damaged expansion valve
- Damaged evaporator
- Worn or stretched serpentine belt (required to operate the compressor and clutch)
As you can see, both systems are very different. However, if you’re experiencing problems from the HVAC controls, then it’s possible that the same issue will prevent both your air conditioning and heater from working. For instance, a failed blower motor won’t be able to blow air into the cabin. A failed fan switch will make it impossible to adjust the blower fan speed. There are a number of other potential issues, ranging from a failed relay to a blown fuse to a short in the wiring.