REFERENCE · LIVE
A7 Climate Sensor Map
Every climate-control input sensor on a modern ATC system. Role, normal value, location, and what it looks like when it fails. Start every "weird HVAC behavior" job here.
DIAGNOSTIC ORDER
- Scan tool first — read all HVAC PIDs and compare to reality (IR gun, thermometer).
- Sensor that disagrees with reality is your culprit 80% of the time.
- Backprobe at the sensor to isolate sensor vs harness vs module.
PRIMARY INPUTS
Ambient Air Temp
RoleOutside air temp → sets baseline blower, defrost, A/C decision
Normal±2°F of actual outside temp
LocationBehind grille or mirror housing
Fault footprintRefuses A/C in winter or runs heat in summer; blower stuck on high
TestCompare PID to outside temp; resistance vs temp chart
PRIMARY INPUTS
In-Vehicle Air Temp
RoleCabin temp → compares to setpoint to drive system
Normal±3°F of cabin air
LocationAspirated near dash center, small intake grille
Fault footprintSystem fights setpoint; aspirator fan can fail
TestListen for aspirator; clean intake; PID vs thermometer
PRIMARY INPUTS
Sun Load Sensor
RolePhotodiode reads solar radiation; ATC boosts blower in sun
Normal0V dark → 4-5V direct sun
LocationTop of dash, often with humidity sensor
Fault footprintBlower stuck on high (stuck bright) or no compensation (stuck dark)
TestCover sensor and watch PID drop; clean lens
SAFETY INPUTS
Evaporator Temperature
RoleFreeze protection; cycles compressor off below ~32°F
Normal36-42°F during cooling
LocationEmbedded in evaporator fins
Fault footprintStuck warm = evap ices up; stuck cold = compressor never engages
TestResistance vs temp chart; visual at evap fins (ice or frost)
SAFETY INPUTS
Refrigerant Pressure Transducer
RoleAnalog signal of high-side pressure for compressor and fan command
Normal0.5V at 0 psi → 4.5V at 500 psi
LocationHigh-side line near drier or compressor
Fault footprintCompressor cuts out incorrectly or runs through overpressure
TestCompare PID to manifold gauge; backprobe 5V ref + signal
SAFETY INPUTS
High/Low Cutout Switches
RoleDigital cutoff (not analog) for safety pressures
NormalClosed during normal range, opens at unsafe levels
LocationHigh side: condenser line. Low side: accumulator or low line.
Fault footprintCompressor never engages (stuck open) or no protection (stuck closed)
TestContinuity at known good pressures; jumper test with caution
FEEDBACK
Blend Door Position
RoleClosed-loop feedback of door angle for HVAC module
NormalVoltage sweeps 0-5V across full door range
LocationIntegrated into blend door actuator
Fault footprintActuator hunts endlessly; B-code or U-code at HVAC module
TestScan tool actuator test; replace actuator if no movement or stuck signal
FEEDBACK
Humidity Sensor (windshield)
RoleReads cabin humidity for auto-defog and auto-recirc
Normal0-100% RH; climbs with occupants and weather
LocationTop of dash, often combined with sun sensor and rain sensor
Fault footprintDefog stuck on; recirc auto-mode misbehaves
TestCombined module — usually replace as assembly
SHARED INPUT
Engine Coolant Temp (ECT)
RoleATC reads ECT from PCM to gate heater output
Normal~195-210°F at operating temp
LocationEngine block or thermostat housing
Fault footprintPCM ECT bad = no heat command, blend door wrong
TestDiagnose at ECT sensor (A1/A8 procedure)
CROSS-CHECK CHEAT SHEET
When the system misbehaves, look here first
- Always cool = in-vehicle temp reading too warm; sun load stuck bright
- Always hot = in-vehicle temp reading too cool; sun load stuck dark
- Blower always full = sun load stuck bright; in-vehicle/ambient mismatch
- Compressor never engages = pressure transducer or low-side switch failed open; freeze sensor stuck cold
- Compressor never cuts out = pressure transducer or freeze sensor stuck warm
- No heat in winter = ECT bad (heater locks out); blend door stuck cold
- Defrost always on = humidity sensor stuck high