I own a 1960s classic that is in excellent condition. It runs beautifully and needs little care. However, I have a persistent problem of rising engine temperature whenever I drive with the air-conditioner on. Why should air-conditioning affect engine temperature?
Many cars of that era were not designed to have air-conditioning. Owners would therefore install an aftermarket air-conditioner.
This could be tricky. Besides the space constraint, there are problems in managing the transfer of heat.
Air-conditioners work by removing heat. The warm air in the car or fresh air from outside is fed through an evaporator where a refrigerant absorbs heat, and the resulting cooled air is directed into the cabin.
An air-cooled heat-exchanger known as the condenser dissipates heat into the atmosphere.
In most cases, the condenser is sited between the radiator and radiator grille. An electric fan mounted in front of the condenser provides forced ambient airflow through it.
This fan must be powerful enough to also push air through the radiator. And the radiator must be sufficiently sized to take into account the slightly heated air from the air-con condenser.
Because a car from the 1960s might not have been designed to accommodate an air-conditioning system, all these considerations would not have been taken into account. Hence, engine overheating may occur.
After the circuit breaker, you may want to approach a workshop which specialises in air-conditioning systems to see if some retrofitting work will resolve the issue.