HVAC

Cooling System

Description

Usually used with Automatic Temperature Control (ATC), there are typically three sensors that sense temperature. One sensor is located on the outside of the car to sense outside air temperature. A second sensor is located in the interior to monitor temperature inside the car. The third sensor is usually located in the HVAC ducting, to sense delivered air temperature.

Purpose

The system uses information from the sensors to make decisions on output commands to the HVAC system and the blower motor.

Maintenance Tips/Suggestions

Problems with the HVAC sensors may result in poor regulation of cooling and heating. It is also possible that the speed of the blower motor will not change speed according to system demands. Regardless of the symptom, have it diagnosed as soon as possible by a professional technician.

HVAC Switches and Electrical

Description

An array of wiring, switches, relays and controls. These components may take on dual roles (both a sensor and a switch), where they turn on certain parts of the circuit based on operating conditions. Increasingly, these circuits and controls are integrated with the vehicle's powertrain control module (PCM), even on cars without Automatic Temperature Control (ATC).

Purpose

To electrically manage the HVAC system, based on driver demands and vehicle operating conditions. Cars with Automatic Temperature Control (ATC) provide automatic control over HVAC circuits.

Maintenance Tips/Suggestions

Proper HVAC operation requires normal operation of all parts of the control circuits. As an example, a failed temperature switch may cause faulty erratic or no compressor operation, affecting cooling. Problems with HVAC switches and electrical circuits may cause no cooling, poor cooling, excessive cooling, or erratic temperature control. To determine the root cause, have the A/C system looked at by a professional technician.

vehicle diagram