Eric L.

I was wondering...how does running the AC put an additional load on the cooling system? I mean, there is no coolant in the AC system, only refridgerant. In fact, there is no fluid exchange between the AC and the engine cooling system. The heater core is separate from the evaporator core, although they are integrated into the same unit under the dash. Obviously, running the AC will cause the engine to run hotter. But why? I know RPMS increase slightly with the AC on, but why should that cause the engine to run that much hotter?

This is a great DBM question.

MarkP

Since the a/c condenser is in front of the radiator, air passing over the coils of the a/c condenser is heated up by removing energy from the a/c refrigerant before passing through the coils of the radiator when the A/C is operating, thereby making the cooling system less effective. In a nutshell.

Daniel B. Martin

The engine works harder and this generates more heat to be dissipated by the cooling system.

The engine's radiator is a heat exchanger. It transfers heat from a working fluid (coolant) to the atmosphere. A heat transfer is more easily achieved when there is a big temperature difference between the hot object and the cold object. That's why a marginal cooling system works fine in the winter but not in the summer.

The air conditoner condenser is also a heat exchanger which transfers heat from a working fluid (refrigerant) to the atmosphere.

The condenser is mounted directly in front of the radiator. The fresh air which passes through the radiator must first pass through the condenser. When the air conditioner is working the air which reaches the radiator has been preheated by the condenser. This increases the burden on the cooling system.

Eric L.

Thanks. Good explainations.