I would like to check all input devices to the ECM. I reference the diagram you provided.
1. The red X is the pressure switch you said my Sierra truck doesn t have. Have I crossed out the correct switch?
2A. The A/C request / High Pressure switch is a series grounded circuit that comes from the HVAC control module, through the High Pressure Cutout Switch, and to the ECM Red Pin 55. The switch will open if the pressure is too high. Is this correct?
2B. The A/C Low Pressure switch is a grounded circuit that grounds the ECM Red Pin (Please provide Pin ID). The switch will close when the Freon pressures is too Low. Is this correct?
3. Once the above statements 2A and 2B are proven Grounded the ECM will ground Red Pin 43 which will activate the A/C Compressor Clutch Relay coil. Is this correct?
4. The AC Relay closes providing +12 volts DC to the A/C Compressor clutch, thus engaging the compressor. Is this correct?
List of A/C devices:
-HVAC Control module (only provides a ground via through the High Pressure Cutout Switch)
-A/C High pressure cutout switch (opens when the Freon pressure is too high) circled in green
-A/C Low pressure switch(Closes when the pressure is too low) circled in Green
-A/C Compressor clutch
-TWO 10AMP fuses
-Wires and connectors
What other devices, if any, can be the cause of the A/C relay not to close?
Tuesday, November 3rd, 2020 AT 10:07 AM