Compressor Clutch Control Circuit

September 13, 2019


Compressor Clutch Control Circuit

From Bob Pattengale

Looking at the graph the compressor clutch has a unique relay, it has a compressor control relay that operates in a variety of ways depending upon the application. From the two fuses, one is controlling the coil in the relay (using a 10 amp fuse) that feeds from the relay. The application changes depending if its diesel or gas. If it’s a gas it will separate into SRTs or Except SRTs.        Lower on the graph, there’s a control side and in the case of a diesel it’s called the module. The Module and control will be your PCM (Power-train Control Module), It is another effective way to control the PCM with the module.

What’s going to ground the coil?

What if there was no actuation of the clutch at all? Then a technician has to start with fuses and the control side to validate that its working correctly. Now coming down from the A/C clutch leading to the clutch motor, the power grounds to the other side. Only when the relay is energized would power be available here, and often it’s already has a path to the ground. Nothing on a size not like voltage of sitting here waiting for a ground to occur. This is the positive side, the ground already exists as soon as power is here so we’re going to have that A/C clutch engaged.

Listening to your Bidirectional Control

The A/C clutch is generally pretty easy, just find the bi-directional control then command the A/C clutch on and listen. Pay close attention, was there a clicking or clunking sound? For this particular case, the A/C Clutch is in the ON position. From here, the technician would go out there for pinpoint testing. You may want to double check for any odd sounds because it could be a more serious issue or an exaggeration. This is quick and easy to do for any mechanic.

Moving on, push the button on the AC panel or the AC controls. The HVAC module should see the input, if so the A/C clutch should be engaged. The HVAC module has to send a command to the PCM saying, “The customer would like to AC to be operating, we’d like you to gauge the clutch.” Because now the PCM or Engine Control Module in Diesel engages the ground which then energizes circuit and kicks the clutch in.


[dn_related_product title=”Bosch Advanced Climate Control Systems” description=”The days of simple air conditioning and heating repairs are long gone, which means the strategy for diagnosing these systems need to change. Today’s climate control systems are fully integrated, using a complex vehicle network, with shared modules, sensors and actuators. The answer for the customers concern could be a simple sensor failure or a stuck actuator blend door. This session sponsored by Bosch will help you develop a solid strategy for diagnosing the complete system, which will ensure the issue is diagnosed accurately and efficiently the first time.” link=”/shop/bosch-training/bosch-advanced-climate-control-systems-best-recommended-practices/” image=”/wp-content/uploads/2019/08/WATCH-AN-WIN-TEMPLATE-NO-BOB-_480x320.jpg”]

ASE Accredited