Control Module HVAC: Description and Operation

Typical Power Module Location Under Hood.:

This module controls the operation of the blower motor and is located on top of the evaporator assembly. The power module receives the blower drive signal from the programmer and amplifies the signal to a strong output signal proportional to the input. The power module is transistorized and provides variable blower speeds. If the vehicles interior is hotter or colder than the set temperature, the blower will start at high speed and gradually decrease to low speed as the pre-selected temperature is selected. A heat sink, attached to the power module, protrudes into the evaporator air stream as a means of dissipating heat which the power module generates. The power module, which receives a signal from the programmer, or BCM (some models), also cycles the A/C compressor.

The power module incorporates output circuit protection. If the blower motor or clutch coil draws excessive current, the module will turn "OFF" the output to protect the module and wiring from damage. When the high current condition is corrected, the module will resume normal operation.