Relay 40 is basically the blower motor(s) on/off relay, and when ON results in the highest resistance (and thus greatest voltage drop) to the two blower motors. Each relay across the page bypasses a resistor, until Relay 44 bypasses ALL the resistors and simply feeds 12V directly into the blower motors. Why RR didn't just use a solid state pulse-width modulated output stage is beyond me.
Here's where they're located in your engine compartment (in red):
I'd start wiggling relays and breaking out the VOM. I'd also check common Blower Ground Point 36 there in the engine compartment and buff it up if there's any rust or corrosion.
There are two motors, perhaps one is no longer working. They are located under the bonnet at the left and right side of the cowl. It is also possible that there is an accumulation of debris against the air conditioner evaporator. The back side of the evaporator can be seen by reoving the drivers side (left side) blower housing assembly. Additionally incorrect actuation of the various doors within the climate control housing can cause poor air circulation.
So, Relay 40 is the "ac blower relay" that Bentley Specialists is referring to? I can't seem to get more than 6.6 volts to my blower motors. This relay is energizing, and so are the 41-44 relays.
If the 44 relay is energized and that is supposed to send "12V directly into the blower motors", and at the same time the 40 relay is energized that is supposed to have "the highest resistance (and thus greatest voltage drop) to the two blower motors", then which is it as both are energized? Highest resistance or full 12 volts.
Also, on the 41-44 relays, I notice I can get 11 or 11.5 volts at the 87 terminal, but only 9 volts at the 30 terminal (or vica versa if I'm misremembering).
Would all that depend on the 40 Relay not sending through full voltage because its defective? In other words, I'm trying to figure out the direction of the power flow to the blower motors.
Does the source voltage start at the 40 relay, than that goes on to supply the source voltage for relays 41-44? (or is it the other way around?)
Another odd thing that might show that I'm misunderstanding this, or that it is the other way around - when the car is running, and the A/C is OFF, I can pull relays 41-44 and get voltage (I should have tested how much, I just used my test light that time), on either the 85 or 86 pin (I forget which).
If you are able to clarify this for me, that would be much appreciated, as well as being sure the resistor block is not the issue (I tested this for resistance, and with the meter set on 200, I put the black lead on the left pin of the top three, then touched each of the 4 remaining pins on the plug. I got 0.6, 2.2, 0.3, 1.2.
I guess my question is also, which is the first, simplest thing to try, or relay to replace that would be the source of my blower motors only staying at 6.6 volts? Relay 40?
Mike, that is bloody hard, excuse my french.
My car is a Corniche, I don't have your wiper system, makes it easier. That plastic cover is attached by nuts, a dozen or so. Most of these boxes are cracked and broken around the holes where the bolts go. I repaired mine with fibreglass and repainted. Worked out fine. A new one is 500EUR. They are available from Crewe.
the real issue is where to drill the holes in the newly laid fibreglass. I worked with a cardboard template.
My fans were not powerful at all, this low-cost trick did magic!
In addition, the fans on 1980-1985 cars are actually controlled via a box located under the glovebox on the co-divers side. This box shoots voltage on and off depending on the knob setting and, if on Auto, it can select a large variety of speed settings. So you have something like 50% of AC arriving at the fan, hence normal DC measurements will never give you more than 7 to 8V. Again, 20.000 series cars are different, I understood (but that cracked box remains and issue).
Maybe somebody else wants to chime-in here...