Diagnose Ford Escape AC wiring diagram
Ford Escape AC wiring diagram
This post is about diagnosing and AC problem in a Ford Escape. The 2008 Ford Escape AC wiring diagram is fairly representative of how these systems work.
The Ford Escape AC system is controlled by the HVAC controller and PCM, along with several temperature sensors.
Components used in the Ford Escape AC system
Cylinder head temperature sensor
Engine coolant temperature sensor
Evaporator temperature sensor
Low pressure AC cycling switch
Dual function high pressure switch
How the AC works in Ford Escape
1, Driver selects AC
2. HVAC controller checks evaporator temp sensor. If ok,
3. HVAC controller sends an AC request signal to PCM
4. PCM checks ambient temp sensor—must be above 35°F
5. PCM checks cylinder head temp sensor. Must be below set temp.
6. PCM checks engine coolant temp sensor. Must be below set temp.
7. PCM checks for power from AC low pressure switch in series with high psi switch through ACCS input.
8. PCM checks high psi switch at ACPSW switch inputs from dual function switch.
Low pressure switch is located on the evaporator outlet line
Duel function high pressure switch is located on the receiver drier
11. PCM grounds AC compressor clutch relay control coil which closes relay contacts and sends power to compressor clutch coil.
12. Compressor clutch receives ground at left front corner of engine compartment
13. If PCM sees open at high psi switch, it interrupts ground to compressor clutch control coil AND operates high speed condenser fan. When condenser pressure drops, high psi switch closes and completes circuit to PCM and PCM provides ground to AC compressor clutch control coil to close clutch contacts
Diagnose compressor clutch doesn’t engage on Ford Escape
Step 1: Using a test light, check fuses 27 and 13. If good, remove AC compressor clutch relay from socket.
Step 2: Use test light to check for battery voltage on terminals 2 and 3 in relay socket. If good, relay is receiving power.
Step 3: With engine running and AC turned on, use test light to check for ground on terminal 1 in relay socket. If PCM is providing ground, that confirms all temperature and pressure sensors are within acceptable range. If so, proceed to check relay operation and compressor clutch wiring. If not, skip to sensor testing below.
Step 4: Re-install relay. Disconnect compressor clutch connector. Start engine and turn on AC. Check for battery voltage on one terminal of the connector. If you see battery voltage, check the other terminal for ground.
If you’re not getting battery voltage at the compressor clutch connector and you’ve completed all the voltage checks in steps 1-3, swap in another compressor clutch relay. If you see voltage, old relay was bad. If still no voltage at compressor clutch connector, check for open in wiring harness from relay to compressor.
AC Sensor testing Ford Escape
Using a scan tool with live data, check the status of: Cylinder head temperature sensor, Engine coolant temperature sensor
Evaporator temperature sensor, Low pressure AC cycling switch, Dual function high pressure switch. If any of those sensor readings are outside acceptable range, the PCM will not ground the compressor clutch relay. Remedy the situation before proceeding.
©, 2017 Rick MuscoplatPosted on by Rick Muscoplat
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