Auto A/C Repair/Component Basics

From a previous post I described the basic components of the air conditioner system and how a/c works. We'll go over these and cover a few more components that are related specifically to auto air conditioning.
The Compressor will be mounted somewhere on the front of the car engine and is belt driven. This is the pump that circulates the freon through the a/c system. On the front of the a/c compressor is an electro-mechanical clutch. When power is supplied to it by turning the a/c on, the clutch is energized and the compressor is turned by the engine.
The Condenser is the part of the a/c system that removes the heat from the freon and it is located in the front of the car usually right in front of the engine radiator. It looks like a small radiator or oil cooler.
The Evaporator may be located inside the car usually under the dash. It is contained inside the ventilation box along with the heater core and typically very hard to get to. This component is used to remove the heat from inside the car by recirculating the air over the evaporator coils by way of the blower fan. It looks like a small radiator or heater core. Some vehicles have the evaporator mounted in a ventilation box on the passengers side firewall under the hood. Most General Motors products use this arrangement. Some vans and SUV s actually have 2 evaporators. They have a separate unit for cooling the rear of the vehicle.
One of 3 devices is used to control the flow of freon to the evaporator on most auto a/c units;

1. expansion valve
2. expansion block
3. orifice tube

The expansion valve, if equipped is usually located in the box with the evaporator. It will have a tube with a remote bulb on the end connected to the outlet side of the evaporator.
the bulb senses the temperature of the freon leaving the evaporator coil and the expansion valve regulates the freon flow accordingly.

The expansion block is usually located under the hood , near the firewall where the inlet and outlet lines from the evaporator emerge.It is connceted to both , the inlet and outlet line of the evaporator.

the orifice tube will be inside the inlet line of the evaporator at the firewall where the lines attach to the evaporator.

A high pressure safety switch is generally located somewhere on the compressor. If there is a wire attached to the compressor, ( not to the compressor clutch) this is a hps switch.This switch stops the a/c if the high pressure side exceeds its limits.

A low pressure safety switch is generally located somewhere close to the evaporator.
It will be in the suction side line leaving the evaporator ( the larger line). May also be located on the dryer/accumalator. This switch stops the a/c if freon gets low or the low pressure side falls below its limits.

The dryer/accumalator is usually located close the the evaporator usually on the left side fender close to the firewall. This is used to remove moisture and contaminants from the freon and serves as a storage container for the freon in the system.
note:
Some cars have the dryer by the condensor in front of the radiator. You may also find the hps switch there on some cars.

Most vehicles use either R-12 freon or R-134 freon. R-134 is used to replace R-12 in older cars as it is more environmentally friendly than R-12. If your car is older and still has R-12 in it , It will need to be retro-fitted to use R-134.

I think we've covered the majority of a/c components on most autos of today so we'll move on to A/C Troubleshooting in the next post.