A/C Compressor Throttle Cut-Off Relay (PartTerminologyID 3168): Where PCM-Integrated Inapplicability Note Prevents Orders From Modern Vehicle Buyers
Written by Arthur Simitian | PartsAdvisory
PartTerminologyID 3168, A/C Compressor Throttle Cut-Off Relay, is the relay that de-energizes the A/C compressor clutch circuit when the throttle reaches or exceeds the wide-open throttle position, temporarily interrupting compressor operation during maximum-power acceleration events to remove the compressor's parasitic load from the engine and deliver maximum available power to the drivetrain. That definition covers the WOT compressor cutoff function correctly and leaves unresolved the throttle position threshold at which the relay trips, the activation source from the throttle position sensor signal processed by the PCM or from a direct mechanical kickdown switch, and the re-engagement delay after the throttle drops below the cutoff threshold.
For sellers, PartTerminologyID 3168 is a functional subset relay that on modern PCM-controlled vehicles is implemented as a software function within the PCM rather than a discrete relay. The PCM monitors throttle position continuously and inhibits the A/C clutch relay output when WOT is detected, without requiring a separate relay. The discrete throttle cut-off relay exists primarily on older vehicles with analog throttle kickdown switches where the PCM's A/C inhibit logic was not yet integrated into the engine management software. The listing must state the vehicle's PCM-integrated versus discrete-relay architecture and must note the inapplicability to modern vehicles where this function is a PCM software parameter.
Listing Requirements
PartTerminologyID: 3168
throttle threshold: WOT switch or PCM TPS threshold (mandatory)
activation source: mechanical kickdown switch or PCM output (mandatory)
re-engagement delay specification (mandatory)
PCM-integrated inapplicability note for modern vehicles (mandatory)
application window for discrete relay architecture (mandatory)
OEM part number cross-reference (mandatory)
FAQ (Buyer Language)
Does my modern vehicle use a separate throttle cut-off relay?
No. Modern PCM-controlled vehicles implement the WOT A/C cutoff as a software function. The PCM monitors throttle position and inhibits the A/C clutch relay output directly without a separate relay in the circuit. This discrete relay applies to older vehicles with analog kickdown switch architectures.
What the A/C Compressor Throttle Cut-Off Relay Does
The A/C compressor throttle cut-off relay de-energizes the A/C compressor clutch circuit when the throttle reaches or exceeds the wide-open throttle position, temporarily interrupting compressor operation to remove its parasitic load from the engine and deliver maximum available power to the drivetrain during full-power acceleration events. The relay receives its activation signal from either a mechanical throttle kickdown switch that closes when the throttle linkage reaches the WOT detent, or from a PCM output on early electronic throttle management systems that had not yet integrated the WOT A/C inhibit as a software function. When the throttle drops below the WOT threshold, the relay de-activates and the compressor clutch re-engages after a brief delay to prevent compressor surge from abrupt re-engagement at high engine speed.
On modern PCM-controlled vehicles the WOT A/C cutoff is implemented entirely as a PCM software function. The PCM monitors throttle position through the throttle position sensor signal and inhibits its A/C clutch relay driver output when WOT is detected, without any discrete relay in a separate throttle cut-off circuit. There is no relay socket, no relay mounting position, and no separate throttle cut-off wiring harness circuit on these vehicles. Buyers who find the A/C stops working at full throttle on a modern vehicle are observing the PCM's intentional WOT inhibit software function operating correctly, not a throttle cut-off relay fault.
Why This Part Generates Returns
Buyers return A/C compressor throttle cut-off relays because the vehicle is a modern PCM-controlled application where WOT inhibit is a software function and no discrete relay exists, the mechanical kickdown switch that activates the relay has failed and the replacement relay receives no activation signal regardless of throttle position, and the relay is delivered for the correct application but the A/C clutch coil circuit has an open fault that prevents compressor engagement even after the throttle cut-off relay is confirmed functional.
Final Take for PartTerminologyID 3168
A/C Compressor Throttle Cut-Off Relay (PartTerminologyID 3168) is a legacy discrete relay architecture associated with vehicles from approximately the 1970s through the early 1990s where WOT A/C inhibit required a physical relay rather than a PCM software output. The PCM-integrated inapplicability note for modern vehicles is the mandatory first attribute because it redirects the majority of buyers who search for this relay toward the correct understanding that their vehicle's WOT A/C cutoff is a PCM calibration function, not a relay fault. Throttle activation threshold, re-engagement delay, and application window are the three supporting attributes for buyers confirmed to have a discrete throttle cut-off relay circuit on their specific vehicle.
Listing Requirements
PartTerminologyID: 3168
throttle threshold: WOT mechanical switch or early PCM TPS output (mandatory)
activation source: kickdown switch or PCM output (mandatory)
re-engagement delay specification (mandatory)
application window: discrete relay architecture approximately 1970s through early 1990s (mandatory)
PCM-integrated inapplicability note for modern vehicles (mandatory)
OEM part number cross-reference (mandatory)
My A/C stops working at full throttle on a modern car. Is the relay failed?
No. On modern PCM-controlled vehicles this is the PCM's intentional WOT A/C inhibit software function operating correctly. The PCM monitors throttle position and inhibits its A/C clutch relay driver output at WOT without any separate relay. The A/C restores when the throttle drops below the WOT threshold. No relay replacement is required or possible for this function on modern vehicles.
How do I test the throttle kickdown switch that activates this relay?
With the ignition on, measure voltage at the relay coil terminal with the throttle at idle and again with the throttle held at wide-open position. Coil voltage should be absent at idle and present at WOT. If coil voltage is absent at both positions, the kickdown switch is failed or its circuit has an open fault. If coil voltage is present at both positions, the switch is stuck closed and the A/C will be inhibited at all throttle positions regardless of relay condition.