Chart C10C - A/C Constant Run Relay Check
A/C constant run relay is used to keep the A/C compressor from cycling at idle for 3 minutes. The relay by-passes the A/C pressure cycling switch when energized. The relay has a normally open set of points allowing normal A/C clutch cycling. The relay coil is supplied 12 volts by ignition and the ECM completes the circuit to ground when idle is detected. This closes the points and by-passes clutch cycling for 3 minutes.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- This test checks for no A/C clutch cycling at idle for 3 minutes.
- This test checks to see if A/C clutch operation is being controlled by the A/C constant run relay of the A/C cycling switch. If the compressor remains engaged after A/C cycling switch connector is removed, fault is in relay or false ECM signal to energize relay.
- By connecting a test light across the relay connector coil terminals, it can be determined if fault is a bad relay (test light off) or grounded ECM circuit or ECM (test light on).
- Connecting a test light across the relay connector coil terminals, it can be determined if fault is from lack of signal to relay (test light off) or a faulty relay (test light on). With the ignition on and test terminal grounded, ECM will energize the relay.