Engine overheat is a condition where the engine's temperature rises above the normal operating temperature. This can lead to engine damage.
Air conditioner is a system that cools the cabin of the vehicle by removing heat away from it. The air conditioner is powered by the engine.
The cooling system removes heat from the engine by using coolant to remove the heat and then transfering the heat to the environment through the help of radiator and radiator cooling fan.
The common overheating condition related to air conditioner is that of engine overheating which occur whenever AC is in use. The scenario we are discussing in this article is that of overheating which occur when the air conditioner is not in use but stops when the AC is turned on.
In the case of the engine overheating when AC is turned on, it is caused by any of the following:
1. Faulty AC compressor that places excessive load on the engine.
2. Faulty Auxiliary cooling fan. In most cases, the auxiliary cooling fan turn ON when the AC is being used but if it doesn't work, the main cooling fan operation is not enough to cool the engine.
3. Inefficient cooling system as a result of leakage, blockage, corrosion, broken fan blade, broken fan shroud and so on.
How radiator cooling fans in cars with AC work.
In order to provide adequate cooling when air conditioner is being used, there are two different kinds of fan setup:
1. Main and auxiliary radiator fans setup.
In this setup, the main fan is the primary fan responsible for cooling the engine. The auxiliary fan kicks in only when AC is turned on or when more cooling is required by the engine due to factors like high ambient temperature, high speed and high load.
2. A single fan with high speed for more cooling when AC is turned on.
The single fan has variable speed. The speed of the fan goes high when AC is in use, in order to provide more cooling. This is achieved with the help of fan speed control module/circuit which can be relay or solid state electronic types.
What makes engine to overheat but stop to overheat when AC is working?
This overheating situation is caused by radiator fan issues in the following ways:
1. Faulty main/primary fan.
When the main fan is not working, there is no cooling because the auxiliary fan is not yet in operation until the air conditioner is turned on.
In some vehicles, the auxiliary fan is smaller and in the event of main fan failure, it kicks in whether AC is working or not but may still not be able to cool effectively. In this case, turning AC ON won't stop the overheating, though it won't be as severe as when no fan is working at all.
2. Faulty fan module/control circuit.
When there is a fault in the circuit that controls the main fan but that of the auxiliary fan is okay, the engine will overheat when the AC is not in use. This can be a relay, resistor, solid state electronics or other circuit fault.
3. Bad fuse.
If the fuse protecting the primary fan is bad, the engine will overheat when AC is not functioning.
4. Faulty low and/or medium speed fan mode.
In some vehicles, it is the AC that triggers the high speed operation of radiator fan. When there is an issue with low/medium speed operation probably due to an issue with a part or component of the fan control circuit, the radiator cooling fan will only work when the air conditioner is turned on.
In conclusion, remember that for a two fan configuration, this type of engine overheating happen when the primary fan is faulty and the AC triggers the operation of the secondary fan. For a one fan configuration, it is when the low/medium fan speed is faulty and the AC triggers the high speed operation.
Some people try to solve this issue by doing direct fan connection to power source but it is not a good solution and it has a lot of disadvantages such as increased fuel consumption, shortens fan lifespan, wears the engine faster, excessive fan noise, attracts dust and debris that can affect some parts of the engine, increased electrical load which can affect alternator and battery and has safety issues.