ac fan blower no speed

[fadyeid]

hello everyone

I need to know how the fan blower inside a car woks with speeds , because inside the blower there is a circuit but welded on a metal it has two big transistors , so could I build a circuit to replace this if yes need a simple circuit by 4 speed and off  ?! thanks

[Zero999]

The metal acts as a heat sink for the transistors. You could easily use your own circuit to control them, thus the motor speed, if you want to.

[cs.dk]

so could I build a circuit to replace this if yes need a simple circuit by 4 speed and off  ?! thanks

Why build a replacement?
The module you show looks like a PSA (Peugeot/Citroën) type - I have replaced alot of these transistors. MJ11015 or MJ11016 are replacements. Some modules are PNP, others are NPN.
Some modules are controlled in "opposite" direction. 0V = full speed, 12V = stop.

The module it self is not with 4 steps in fan speed. The climate controller drives the fan motor at the necessary speed all time.

[Zero999]

so could I build a circuit to replace this if yes need a simple circuit by 4 speed and off  ?! thanks

Why build a replacement?
The module you show looks like a PSA (Peugeot/Citroën) type - I have replaced alot of these transistors. MJ11015 or MJ11016 are replacements. Some modules are PNP, others are NPN.
Some modules are controlled in "opposite" direction. 0V = full speed, 12V = stop.

The module it self is not with 4 steps in fan speed. The climate controller drives the fan motor at the necessary speed all time.

How old are those cars? I'd be surprised if a modern car uses Darlington transistors, rather than MOSFETs to control the blower.

[fadyeid]

yes they are for Psa cars , so you mean the two transistors play a role to change speed ? so any blower has a fault with speed caused by this transistors ?

[cs.dk]

@Hero999, these modules are used in mid/late 90's cars. ex. Citroën Xsara, Xantia, Peugeot 406 that i know of. They often fail short, and the blower then runs at full speed.
Afaik they are only fitted in cars with AC, so the climate ECU can control the blower speed. Non AC cars have the usual resistor-pack, and 4 fixed speeds.

@fadyeid, Yes if the speed can't be regulated, the transistors are shot.
Note, if you replace them, there is a little disc thermistor between the heatsink and PCB, it is very easy to loose when you're busy replacing the transistors.