This part of site is an attempt to organize and add to the web resources for the Rover SD1
to form a cohesive and easily usable guide for those of us without easy access to
expert repair and/or advice. It is not offered in any way as a definitive source
and we take no responsibility for any errors that may exist.
Webmaster Rene Winters
The Rover SD1 Airconditioning|
The Electrical Circuit
Now the electrical circuit it controls the operation of the compressor electromagnetic
clutch the condensor cooling fans the blower fans and the heated backlight.
First let's consider the clutch circuit. With the mode selector in the max, normal,
Bi-level or defrost positions, the mode microswitch arrowed, is operated by a cam on
the vacuum divertor.
It supplies current to this on/off micro-switch, which is operated by the fan speed
selector, through the vacuum switch. Providing the fan speed selector is not in the
off position, and the outside temperature is above freezing point, current from
the 'on/off' microswitch passes through this ambient temperature switch and energises
the magnetic clutch relay, arrowed. The positions of these relays could vary,
so always confirm the identity of a relay by the colours of its connecting cables.
The relay completes the circuit through this thermal limiter to the clutch windings,
causing the compressor and therefore the refrigeration system to operate.
To improve the cooling rate of the condensor, two electric cooling fans are fitted.
They are forward of the engine coolant radiator.
The fans are controlled by this high pressure switch and are energised via this
relay adjacent to the starter relay.
The high pressure switch closes whenever the refrigerant pressure, from the condenser,
measured at the V.I.R. unit, exceeds a critical level. The blower fans will not
normally operate unless the heat load is extremely high, as adequate cooling,
for normal conditions, is provided by the engine driven fan.
Now the blower fan circuit. Speed variation is achieved by completing
the blower motor earth path through decreasing resistances. The earth path is
direct at speed 4.
Incidentally fan speed 4 is unavailable whenever the heated backlight is on.
The heated backlight can only operate in the vent, heater or defrost modes.
By depressing the panel mounted switch. Current from the mode microswitch 1, or the
defrost microswitch 2 energises the backlight through the relay 1. At the same time
the heater resistance bypass relay 2, is also energised.
If the heated backlight is switched on, when the blower fan is operating at
speed 4, its speed is automatically reduced, as the bypass relay re-routes
the earth path, through the third speed resistor.
If the heated backlight is switched on, when the blower fan is operating at speed 4,
its speed is automatically reduced, as the bypass relay re-routes the earth path,
through the third speed resistor.