Blower Fan Speeds.
 

Hello,
I no longer have the Low and Medium Fan Speeds on my heating module (High OK) 1993 XJ6 Sovereign 4.0 ltr 6. Would welcome any input.

Thanks,
AlinBC.

Hi Al,

The most common cause of loss of Low and Medium fan speeds is a problem with the speed control circuit boards inside the blower motor housings, which contain a Darlington power transistor, a power resistor, and a couple of diodes. Replacing these components usually restores proper operation.

For the High speed, relays bypass this circuit boards and apply battery/alternator voltage to the fan motors, so that's why your High speed still works. For a full explanation and solution see the XJ40 Book at Jag-Lovers:

Jag-Lovers XJ40 Book: Air Con Blowers

Cheers,

Don

Thanks Don, I appreciate your input. I've been reading up on the very same. I have the Haynes manual, removal of these units seems to be a trial but I think I can handle it. I replaced the AC Evaporator Rad 10 years ago..............nothing could be worse than that.
Many Thanks for your advice,
AlinBC CANADA.

May 9th 2019

Don,
I removed both blower packs and replaced all components (Relays,Transistors, Diodes, Resistors, Capacitors and motor brushes) irrespective of whether they tested good or bad, I didn't want to do that job again. Clearly one of the units had been out of service for some time (motor brush length indicated such). Working perfectly now.
Thanks Again,
AlinBC.