P0645: How to Diagnose & Fix — A/C Clutch Relay Control Circuit

The Omron A/C clutch relay (Honda part 39794-SDA-A03) is defective and gets hot, causing failure. Honda-specific part with reduced coil current known to be problematic. When relay fails, either battery dies overnight (relay stuck closed) or AC stops working (relay stuck open). Low refrigerant from pressure relief valve venting can lead to failed AC compressor.

8th generation Accords (especially V6) commonly lose A/C because the compressor clutch fails to engage. The magnetic clutch coil opens (loses continuity) or the clutch air gap widens with wear, so the clutch plate no longer pulls in when the A/C is requested - the compressor pulley spins but the compressor never turns. A failed high/low pressure switch or the 7.5A MG-clutch fuse can produce the same no-engage symptom. The result is warm air from the vents even with a full refrigerant charge. This is the compressor-clutch engagement failure, distinct from the refrigerant-loss condenser-leak issue.

The Dodge Challenger has a well-documented tendency to stall or shut off completely without warning while driving — a top-3 engine-category complaint at NHTSA and one of the most-reported electrical/engine problems at CarComplaints. There are two primary, separately documented root causes that present the same symptom. (1) ALTERNATOR FAILURE (3.6L Pentastar, and later 5.7L/6.4L with electro-hydraulic power steering). Chrysler began investigating stalling complaints on 2011-2012 Dodge Chargers in August 2014 and found thermal fatigue of the silicon diodes inside the alternator. The large, intermittent current draw of the electro-hydraulic power-steering (EHPS) pump thermally stresses the diodes until the alternator fails suddenly. This became NHTSA recall 14V634 (Chrysler P60), covering ~434,000 2011-2014 Chrysler 300, Dodge Charger, Challenger, Durango, and 2012-2014 Jeep Grand Cherokee vehicles with the 3.6L engine and 160-amp alternator (remedy began Feb 27, 2015). It was later expanded under NHTSA recall 17V435 (remedy began Feb 12, 2018) to additional 2011-2014 cars with EHPS and 5.7L or 3.6L engines. NHTSA's stated consequence for both: "If the alternator fails, the vehicle may stall without warning, increasing the risk of a crash," with an additional risk of an underhood fire from a short circuit. (2) TIPM (Totally Integrated Power Module) / FUEL-PUMP-RELAY FAILURE (2008-2014, all engines). The TIPM is the car's central fuse/relay/electrical-distribution computer. When it (or its internal fuel-pump relay) degrades, owners report the engine stalling or shutting off mid-drive, intermittent no-starts, flickering lights, and multiple simultaneous warning lights (check engine, traction control/ESC, ABS). CarComplaints documents this on the 2009 Challenger ("engine shuts down while driving," 7 complaints, severity 8.6/10, ~$800 average repair, ~43,300 miles) and the 2013 Challenger ("bad TIPM," 12 complaints, severity 7.2/10, ~$940 average repair, ~43,050 miles). Because the engine quits unexpectedly, the driver loses power steering and (on automatics) power braking assist while the car is in motion — making this a genuine safety hazard, especially in intersections, on highway merges, and during turns. Multiple NHTSA complaints describe near-crashes and crashes from sudden loss of power.

The Murano A/C compressor clutch is prone to failure, particularly on the first and second generation models. The clutch relay, clutch coil, or the compressor clutch bearing can fail, resulting in no A/C cooling. Symptoms often start with intermittent A/C operation — cooling works sometimes but not others — before progressing to complete failure. A seized compressor clutch bearing will produce a constant squealing noise with the A/C off.