Please, any help would be appreciated, I have wracked my brains and asked some smart people and each has had an idea or two but without results.

The problem.
Two years ago in the fall, the heater/AC would stop and restart all on its own. I ignored it and decided to look at it in the winter, well I never did and never bothered really last year as I hardly used the car, less than 500 miles all last year and this year to date.

Well, this year I decided to solve the problem, while I was just looking at the fan regulator the fan suddenly went up to top speed and was only stopped by pulling fuse #37. The fan starts as soon as the key is turned to the on position.It has got to be something simple, at the moment I can vary the heat and AC temperature but I cannot vary the fan output speed which is always at full speed.

I have tried another new cheap fan regulator (resistor), another used BCM and another used heater control module, all three parts at the same time, each individually and combinations of the three in conjunction with the original parts The BCM has the same part, software and hardware numbers on it, the only difference is the manufacturing date.

No configuration of components eliminates the constant 12-volt output at the centre pin to the regulator which should be variable from 2 to 7 volts approximately.

There are three pins to the regulator which should supply a ground, a constant 12 volt and a variable voltage at the centre pin.

The problem lies upstream on the centre pin somewhere, the trouble is the wires coming from the regulator and controller disappear behind the dash.

For the next step, I shall try to trace the centre pin wire and reinstall the original parts which will be a pain in the ar$e.

What made the system go from normal but intermittent operation to a constant full blast from the fan while the temperature selected still operates correctly? Could there be a shorted circuit somewhere or a faulty part I am not considering?

Knowing squat about electronics I am at a complete loss.

I take plenty of rest for my back so this could take some time.

Thanks for your time reading this post.