Ford Scorpio 95+ Air Conditioning Electrical Systems
The Ford Scorpio 95+ may have either Air Conditioning or Climate Control referred to as Semi Automatic temperature control (SATC) by Ford. This article mainly is concerned with the electrical systems that control the air conditioning, and is applicable to both models with and without SATC. However we do not concern ourselves here with the operation of SATC or the Heater Control panel.
The air conditioning is switched on via the switch on the heater control panel or via the SATC system; note although the user can turn the air conditioning off with a SATC system, its default is always on. When switched on current flows to the De-Ice Switch, the De-Ice switch is either open or closed dependent on the temperature of the Evaporator Core.
The De-Ice switch cycles between on and off states to maintain an average Evaporator Core temperature, as it turns on and off the compressor. When closed current flows through the De-Ice switch to the Refrigerant Dual Pressure switch, sometimes incorrectly referred to as the High/Low Pressure switch. This monitors the pressure of the refrigerant and has two separate contacts. One is used to signal the PCM of a pressure problem, the PCM will then command the Engine Cooling Fans to run at full speed, hence also cooling the Air Conditioning Radiator, or more correctly the Condenser. The second contact interrupts the flow of current in a pressure fault, hence turning off the compressor.
Note, Scorpios with the fans running fast all of the time may have an air conditioning fault such as a refrigerant problem or a blockage.
Refrigerant Pressure Switch
Next in circuit is the Wide Open Throttle Relay (WOT), this relay is located in the Auxiliary Fuse box Relay R24 and is energised via the PCM when it detects full throttle. When full throttle is detected the WOT is activated switching off the compressor and allowing maximum engine power to the drive chain.
Finally and last in line is the Compressor Clutch coil, this engages the compressor to the drive belt when energised. A “flywheel” or back emf diode is wired across the coil to shunt the high voltage generated when the magnetic field collapses.
If the compressor is not engaging and an electrical problem is suspected, the following may help. If you suspect it’s a mechanical problem with the clutch you may wish to try step 6 first to try and prove this.
Before proceeding, please ensure you understand how the cycling system works, noting that the compressor does NOT run continually.
1. Fuse Locations
2. Check the supply from the Heater or SATC panel to the De-Ice Switch
Locate the De-Ice Switch in the engine bay.
Location of De-Ice Switch
The De-Ice Switch is located to the left of the Evaporator Housing (RHD), the picture above shows the De-Ice Switch and its inline connector, also the Thermistor that senses the Evaporator Core’s temperature can be seen (bottom left of the picture). The second connector and wiring plugged vertically in, is for the Re-circulation Solenoid.
Pin-Out of De-Ice Switch Connector (Loom Side).
With Air Conditioning switched on and De-Ice Switch disconnected, measuring at the Loom Side of the connector,
a) Between Pins 3 (- test lead) & 4 (+ test lead) a nominal 12V should be measured.
b) Between Pins 3 (- test lead) & 2 (+test lead) a nominal 12V should be measured.
c) If you do not measure a supply as above measure between a good GND (Chassis) point and Pin4.
If no supply is found with measurement a, b & c No supply is available at Pins 4 & 2 (these are commoned together in the loom) and fed directly from Fuse F33.
If no supply is found with a & b, but c proves to be at 12V, then the switched ground from either the SATC module or the heater control panel is missing. This indicates either a loom or connector fault, or a faulty SATC module (however this is very uncommon). Or in the case of a non-SATC model the heater panel air conditioning fan speed selector switch or heater end switch. Also non-SATC systems use Relay R28 (Heater Blower Relay).
3. Bypass The De-Ice Switch
If test 2 a, b & c prove ok, then you may wish to temporally bypass the De-Ice switch.
Turn off the ignition with the connector still disconnected, carefully insert a link on the loom side connector between pins 1 & 2, make absolutely sure nothing can short when the engine is started etc. Turn the engine back on and ensure Air Conditioning controls are to on. Check to see if the compressor now engages, you can leave the engine run, however if the air conditioning is running the Evaporator Core will eventually ice up, this will not cause any damage.
If this test proves positive, either the De-Ice Switch is faulty or possibly the Thermistor is not seated in the Evaporator Core correctly.
4. Dual Pressure Switch
Providing the De-Ice switch is ok, or you have temporally by-passed it and the air conditioning compressor is still not running.
Pressure Switch, located on the Dryer.
Pressure Switch connector in loom (RH side of front cross member RHD).
Pin-Out of Pressure Switch (Loom Side).
The Pressure Switch is located on top of the Receiver Dryer, this is positioned under the front plastic cover on the RH side at front of the engine bay (RHD). Its connector is inline and located by the front cross member just to the left of the Receiver Dryer, its assessable without removing the plastic cover.
With the engine off, disconnect the connector, the switch side is the split portion to the right, the loom side is to the left and corresponds to the above pin out and wire colours. Start the engine and ensure air conditioning controls are to on, measuring between Pin 3 and a good chassis ground, you should have a nominal 12V if the De-Ice switch is closed, or bypassed as in Step 3. If not and you know the De-Ice switch is closed or you have by-passed it, then suspect a looming fault.
If you have 12V at Pin 3, we need to know if the Pressure Switch is closed. Turn off the ignition and on the Switch side of the connector Not the Loom side! Check the continuity between Pins 1 & Pins 3, it should be low at less than 1R.
5. WOT Relay
The WOT relay may be faulty, however it’s a known problem that water ingress in the Auxiliary fuse box can cause faults with the connectors in the fuse box, it may also be applicable to investigate this. Water ingress is usually attributed to no battery cover being fitted. The WOT Relay is Relay R24. Its has been reported that re-seating this relay can sometimes resolve the fault. The output of the WOT relay goes through Busbar P1 in the auxiliary fuse box.
6. Clutch Coil
The air conditioning compressor Clutch coil is the final component in the circuit, when energised a “clacking” noise is briefly audible and the compressor drive wheel should rotate. Its normal also for the engine revs to momentarily drop.
Air Conditioning Clutch Coil Connector.
A nominal 12V should be measured across this connector if the De-Ice switch is closed (or by-passed) and no fault exists with the control circuit. You can substitute the coil for a 22W automotive bulb as a final test. DO NOT USE A TEST BULB FOR ANY OF THE PREVIOUS MEASUREMENTS.
Using an OBD2 Scan Tool with Enhanced Manufacturers Codes
Many modern Automotive Air Conditioning systems are highly integrated into the vehicles diagnostic systems. Unfortunately the Scorpio only provides a few signals that are relevant to air conditioning . This is because these signals are directly fed to the PCM. Thee state of a few inputs can be read, including,
Input to the WOT (this doesn’t prove the relay isn’t faulty, only that the PCM is trying to turn it on).
Air Conditioning Pressure Switch (note the switch contains two sets of contacts, one interrupts the compressor the second signals the PCM, in theory one can fail without the other)
Engine Cooling Fans Off, High or Low speed. (If these are high all the time check the condition of the Pressure Switch).
Air Conditioning switched on (Only SATC).
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