Chart C-10A A/C Constant Run Relay Check

Fig. 039 - Chart C-10A A/C Constant Run Relay Check.:

Fig. 040 - Wiring Diagram for Chart C-10A A/C Constant Run Relay Check. VIN E:

CHART C-10A, A/C CONSTANT RUN RELAY

The 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.



1. Checks for no A/C clutch cycling at idle for 3 minutes.
2. Checks to see if A/C clutch operation is being controlled by the A/C constant run relay or 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.
3. By connecting a test light across the relay connector coil terminals, it can be determined if if fault is a bad relay (test light "OFF") or grounded ECM circuit or ECM (test light "ON").
4. By 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, the ECM will energize the relay.