P1622 — A/c control circuit mal

Causes

• Blown A/C fuse
• Faulty A/C compressor clutch or internal connector
• Failed A/C relay
• Open, short or high resistance in A/C control wiring or connector
• Faulty pressure/low‑pressure switch or sensor
• Corroded or poor ground at compressor, relay or module

Symptoms

• MIL (Check Engine) lamp on with P1622 stored
• A/C compressor clutch does not engage or engages intermittently
• No cooling or reduced A/C performance
• No audible relay click when A/C is requested
• Multiple A/C related codes or communication faults may be present

What to check

• Read freeze frame and all stored DTCs with a scan tool; note A/C request/AC ON status and related sensor data
• Visually inspect fuses, relays and A/C wiring harnesses for damage, corrosion or loose connectors
• Check for corrosion or water intrusion at compressor connector and pressure switch
• Listen for A/C relay click when A/C is turned ON; check relay socket for proper voltage
• Backprobe/measure voltage at compressor clutch connector with A/C ON and engine running (or instructed by service manual)
• Measure continuity/resistance of compressor clutch coil (compare to spec) and check ground continuity to chassis

Signal parameters

• Battery supply to A/C relay/coils: ~12 V (key ON)
• A/C clutch coil resistance: typically a few ohms to ~10–15 Ω (consult vehicle spec)
• PCM/BCM control output: either ground switched to energize relay or 0–12V switched signal (manufacturer dependent)
• A/C pressure switch: normally open/closed or 0.5–4.5 V sensor signal depending on type
• When A/C is requested via HVAC controls: A/C request flag = ON; relay control circuit should show activation

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