I am in the process of servicing/rebuilding the blower motors on my 1988 XJS for the following reasons:
Ignition 'on': blowers work in all positions low, auto, high and defrost.
If I turn the blowers to the 'off' position they will not turn off.
If I turn the ignition off, with the blower switch in the off position the blowers turn off.
if I turn the ignition back on the blower motors stay off until I turn it back on.
I was told in a previous post that the cause of this is the Darlington transistor failure.
My plan is to replace all of the components on the circuit board and on a post on the other forum I saw a list of the parts needed from a poster in the UK.
295-179 Darlington Transistor
151-776 2.5W 68 ohm resistor
829-586 0.01 uF Capacitor
261-176 IN 4004 Diode
261- 299 IN 5401 Diode
298-437 Transistor mounting kit
Are these the parts I need and for anyone who has purchased these parts in the USA, please give me the name/s of the suppliers you used.
Does anyone know how to test the individual components and what values I should see when testing?
Thanks.

 

For those of you who are interested, I ordered these parts from ELLIOT'S ELECTRONICS in Arizona.

Darlington Power Transistor TO3 MOTOROLA DATE CODE 9531 MJ10016 $15.00 $30.00 2

3W 68 OHM 5% METAL FILM - 2 PACK 3W068 $2.69 $5.38 4

.01uf 50V CAPACITOR Dipped Metalized Film.01/50 $0.80 $3.20 4

DIODE 1A 400V 1N4004 $0.40 $1.60 4

DIODE GEN PURP 100V 3A 1N5401 $0.60 $2.40 4

Diode Switching 100V 0.301N4148 $0.40 $1.60

 

Sanchez, I'm sorry I can't advise on how to properly test the individual components, but I'm interested to see how you get on with this project.

When you say your blowers work on low, auto, high and defrost, does the fan speed change at each setting or is it a constant high speed? If the fans are always on high speed no matter the mode switch setting, I've read that's frequently caused by a failed Darlington transistor. If the fan speed varies as it's supposed to, but they won't turn off properly, I might also suspect a failed mode switch or maybe even the ECM acting up.

I only had high speed on my '87 MkIII system regardless of the mode switch position, although my system did turn off when turned to off. I still had the same issue (only high speed fans regardless of setting) after having both blowers rebuilt by Coventry West, I even had them re-test the blowers and confirmed the darlington transistors weren't the issue. I swapped in a different ECM and that solved the problem for a while but now that seems to be acting up and I'm getting inconsistent operation.

Good luck.

 

@Noah: thanks for responding. It seems to me that this is a very difficult topic or very few members have had the MK 111 experience.
To clear the air here is exactly what is going on with mine.
Key 'ON' blower motors go thru all the different speeds. LOW; AUTO; HIGH and DEFROST.
When I turn the switch to 'OFF' the blower motors do not turn off, they stay on low speed.
When I turn the key to the 'OFF' position, the blower motors turn off.
If I leave the blower motor switch in the 'OFF' position and turn the key 'ON' the blower motors stay off
From what I understand about the MK 111 system;
**Failed Darlington transistor = High speed only.
**Failed Relay = only lower speeds assuming the transistor is okay.
Maybe I am totally wrong and I hope someone will correct me if I am.
Repeating, my blower motors respond to the various speed selections as they should.
Based on the above ** the Darlington is good because I get all the different speeds and the relay is good.
The possibility of the ECU being the cause nof the blower motors not turning off is real.
Also, when I turn the key 'on' I get the momentary puff which is normal.
However, I am still going to rebuild the circuit boards because I have 4 sets of parts. (I bought extra just in case and also the price was reasonable)