Chart C-10 A/C Clutch Control Circuit Diagnosis

Chart C-10 (1 Of 3):

Chart C-10 (2 Of 3):

Chart C-10 (3 Of 3):

A/C Clutch Control Circuit:

CIRCUIT DESCRIPTION
The A/C clutch control relay is Powertrain Control Module (PCM) controlled to delay A/C clutch engagement after the A/C is turned "ON." This allows the PCM to adjust engine RPM before the A/C clutch engages.
The PCM will engage the A/C clutch any time A/C has been requested unless any of the following conditions exist:

- High coolant temperature.
- Low battery voltage.
- High A/C system pressure.
- Low evaporator temperature.
- High engine RPM.
- Low A/C system pressure.

When the HVAC control assembly is placed in the A/C mode, a 12 volt signal is sent to the PCM. When the PCM receives this signal the PCM will ground CKT 459 to energize the A/C relay. This will be displayed on the Tech 1 as A/C request "YES." Two separate A/C refrigerant high and low pressure switches are used to monitor A/C system pressure. If the A/C refrigerant pressure is greater than 414 psi or lower than 38 psi, the A/C clutch will not engage.
The A/C refrigerant pressure switches are using DTC 123, 125, 126. If the A/C refrigerant high pressure switch signal wire becomes open, shorted to ground, DTC 125 will set. If the A/C clutch engages and no pressure change is detected, a DTC 123 will set.
The PCM also monitors A/C evaporator temperature. The PCM utilizes this information to cycle the A/C clutch. If A/C evaporator temperature is out of range (high or low), the PCM will disable the A/C clutch relay.
The A/C evaporator temperature sensor uses DTC 120. If the A/C evaporator temperature sensor circuits becomes open, shorted to ground or shorted to voltage, DTC 120 will set.
When a request for A/C has been detected by the PCM, the PCM will ground the A/C clutch control relay driver circuit, the relay contacts will close, and current will flow through the relay to the A/C compressor clutch.
When A/C request has been detected by the PCM, the cooling fan(s) will be turned "ON" unless vehicle speed is too high.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks the PCM's ability to control the A/C clutch control relay.
2. Before replacing A/C control components, refer to Heating and Air Conditioning.
3. Checks for grounded CKT 459 to PCM.
4. If 5 volt reference is not present at the A/C evaporator temperature sensor, the A/c evaporator temperature would be at a fixed value. This would cause A/C clutch to be engaged at all times when A/C is requested.

DIAGNOSTIC AIDS
Before using CHART C-10, be sure no DTC(s) are stored. The PCM will not activate the A/C clutch with a stored DTC.