How do I test the A/C compressor clutch diode?

Per step A18, check for continuity between the terminals of the A/C compressor clutch diode in both directions. If continuity is indicated in one direction and no continuity in the other, the diode is good (go to A19). If not, install a new A/C compressor clutch diode.

What resistance should circuit 31-CA7 (BK) show to ground at diode connector C972 pin 1?

Less than 5 ohms. If resistance is less than 5 ohms, go to step A18; if not, repair circuit 31-CA7 (BK) and test the system for normal operation.

What should be done if the A/C compressor clutch diode shows continuity in both directions?

Install a new A/C compressor clutch diode and test the system for normal operation.

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Ford A/C Compressor Clutch Diode Test A18-A19 - Circuits 31-CA6/31-CA7 Diagnosis

Pinpoint test service procedure screenshot for A/C compressor clutch diode resistance check

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Service procedure pinpoint test showing step-by-step instructions and meter figures for checking the A/C compressor clutch diode resistance and continuity.

AI caption January 2005 · Photo 29 of 56

This document is a screenshot of a Ford dealer technical service website (fordtechservice.dealerconnection.com) showing a portion of an A/C system pinpoint diagnostic test procedure. It covers steps in diagnosing the A/C compressor clutch circuit. Step 2 of one test directs measuring resistance between A/C compressor clutch diode connector C972, pin 1, circuit 31-CA7 (BK, black wire) and ground; less than 5 ohms passes to step A18, otherwise circuit 31-CA7 must be repaired. Step A18, 'CHECK THE A/C COMPRESSOR CLUTCH DIODE,' instructs checking continuity between the diode terminals in both directions — continuity in one direction only indicates a good diode (go to A19); otherwise install a new A/C compressor clutch diode. Step A19, 'CHECK CIRCUIT 31-CA6 (BK) FOR OPEN,' begins with measuring resistance between A/C clutch solenoid connector C952, pin 2, circuit 31-CA6 (BK) and ground (the rest of this step is cut off). Illustrations GL1653A and GL1654A show ohmmeter hookups for the measurements. A reader learns the exact connector pins, wire circuit numbers/colors, pass/fail criteria, and repair actions for testing the A/C compressor clutch diode and related ground circuits.

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Frequently asked questions

How do I test the A/C compressor clutch diode?: Per step A18, check for continuity between the terminals of the A/C compressor clutch diode in both directions. If continuity is indicated in one direction and no continuity in the other, the diode is good (go to A19). If not, install a new A/C compressor clutch diode.
What resistance should circuit 31-CA7 (BK) show to ground at diode connector C972 pin 1?: Less than 5 ohms. If resistance is less than 5 ohms, go to step A18; if not, repair circuit 31-CA7 (BK) and test the system for normal operation.
What does test step A19 check?: A19 checks circuit 31-CA6 (BK) for an open by measuring resistance between A/C clutch solenoid connector C952, pin 2, circuit 31-CA6 (BK) and ground.
What should be done if the A/C compressor clutch diode shows continuity in both directions?: Install a new A/C compressor clutch diode and test the system for normal operation.