Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSJAGUAR1985VANDEN PLAS L6-4.2LREPAIR AND DIAGNOSISHEATING AND AIR CONDITIONINGRELAYS AND MODULES - HVACCONTROL MODULE HVACDESCRIPTION AND OPERATIONSERVO CONTROL UNITMODE CONTROL
1985 Jaguar Vanden Plas L6-4.2L
Mode Control
1985 Jaguar Vanden Plas L6-4.2LSECTION Mode Control
Mode Control
Circuit Diagram
Microswitches
Purpose and Operation
To select desired mode of operation. Four microswitches and one vacuum switch are operated by a small camshaft controlled by the selector knob.
On Auto or Low setting the lowest fan speed is "ON" automatically.
Mode Control "OFF"
- There is no heating or cooling taking place.
- Vacuum solenoid is energized placing input flaps in recirculation mode.
- Feeds to both blower fans are disconnected.
- Feed to compressor clutch is disconnected.
- Vacuum feed to vacuum system is off allowing hot water to flow through heater core.
- Screen flaps in closed position (natural position).
- Center dash flap closed.
- No output to front or rear footwells.
Mode Control "ON" Lo or Auto
- Microswitch "C" moves to closed position - allows a feed to amplifier via 1 amp. delay fuse also to water temperature transmitter, and through resistance to in-car sensor, ambient sensor, temperature selector and amplifier terminal 7.
Mode Control "LO"
- Microswitch "D" energizes R1 section of main blower relay which through resistor R1 allows current from fuse # 10 to MED 1 (2nd) speed microswitch on servo control unit camshaft.
Mode Control "HI"
- Microswitch "B" moves to closed position. Allows feed to High/Recirculation microswitch - feeds to main blower motor relay overriding fan relays to give High Speed continuously water temperature switch, water temperature bypass microswitch, Ranco Thermostat low speed relay.
Mode Control "DEF"
- Microswitch "A" moves to closed position - allows feed to recirculation/High speed microswitch. Main blower relay overriding sensing circuit into hot mode.
Microswitch Positions
%>4Air Conditioning Wiring Diagram:
Circuit Diagram
Mode Control Microswitches:
Microswitches
Purpose and Operation
To select desired mode of operation. Four microswitches and one vacuum switch are operated by a small camshaft controlled by the selector knob.
On Auto or Low setting the lowest fan speed is "ON" automatically.
Mode Control "OFF"
- There is no heating or cooling taking place.
- Vacuum solenoid is energized placing input flaps in recirculation mode.
- Feeds to both blower fans are disconnected.
- Feed to compressor clutch is disconnected.
- Vacuum feed to vacuum system is off allowing hot water to flow through heater core.
- Screen flaps in closed position (natural position).
- Center dash flap closed.
- No output to front or rear footwells.
Mode Control "ON" Lo or Auto
- Microswitch "C" moves to closed position - allows a feed to amplifier via 1 amp. delay fuse also to water temperature transmitter, and through resistance to in-car sensor, ambient sensor, temperature selector and amplifier terminal 7.
Mode Control "LO"
- Microswitch "D" energizes R1 section of main blower relay which through resistor R1 allows current from fuse # 10 to MED 1 (2nd) speed microswitch on servo control unit camshaft.
Mode Control "HI"
- Microswitch "B" moves to closed position. Allows feed to High/Recirculation microswitch - feeds to main blower motor relay overriding fan relays to give High Speed continuously water temperature switch, water temperature bypass microswitch, Ranco Thermostat low speed relay.
Mode Control "DEF"
- Microswitch "A" moves to closed position - allows feed to recirculation/High speed microswitch. Main blower relay overriding sensing circuit into hot mode.
Air Conditioning Wiring Diagram:
Microswitch Positions
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.