Okay, I assume you can all get the blower motor assembly out of the car no problem. This was done on a 91 NA.

First, remove the blower motor and housing....

You can see the clips that hold the unit together, They are easily removed with a flat head screw driver... There is also one screw that needs to be removed... see below



Once those clips and that single screw has been removed, The unit will come apart into two pieces... Below is the lower half that contains the power transistor we will be replacing...

Remove the 2 screws that hold the metal cover onto the housing...



Cover Removed.....

Flip it over and remove the 2 screws that hold the transistor and heat sink in place.



The transistor assembly will drop right out...



Remove the 2 screws that hold the plastic case on...

Now, you MUST unsolder the connections... it helps to use a very small flat head to help pry the contacts away once the solder is melted.... Once you have all 3 joints free, you can remove the 2 screws that hold the plastic part to the heat sink.

Connector, capacitor, and connection points to transistor removed....


View of heat sink with connector assembly removed...

Only now should you remove the 2 screws that hold the transistor to the heat sink. One of them h as a nut that will have to be held in place to remove. (thats why we removed all the solder joints and plastic part first.. to get to the nut...)


Old blown transistor next to brand new Digikey replacement...


Bolt the new transistor back in place replacing both screws and the single nut.


Reattach the connector assembly, resolder all joints, and assembly is the reverse of removal.. WORKS GREAT!!!

Digikey Part Number:

P/N MJ11016GOS-ND
Desc trans darl npn 30A 120V T03
$3.72 + ship<br><br><br>hopefully this will ease the pain for some poor rx7er in the future....<br>

 

nicely done, this should be archived.

 

pics are a bit fuzzy, but great job.

why would one need to replace this resistor though? Does it make the blower not turn on if its blown?

 

+1 archive.

 

This is not a resistor, it is a transistor... it controls the fan speed except when on high. There is a nice relay in there that kicks full power to the motor. Symptoms of failure are that your AC fan only has 2 speeds, off and high.

 

So originally my blower motor did not work and its brand new. So I resodered the connections on the cpu circuit board. Then I got the blower to work but only on max speed. So then I checked out the power transistor and it seemed fine. But I still resodered the connects around it and repairs mouse chewed wires. Then hooked it back up again and it worked! It worked on max but when I adjusted the fan speed it slowed down a little. But not as much as it should be when the fan was set to low. I do have a new logicon installed so I figured it can't be that. Unless what ever the small blackbox which is attached to the logicon is bad. Anyway I was excited for about 5 minutes and then the blower motor stopped working completely. Please help I would like to have heat and a/c in my car.

 

trickdrift,

You are just going to have to take a volt meter and check voltages from the logicon, at the relays, at the blower motor itself, relays, and grounds. The schematic for the motor and all the relays are in the FSM. There is only one way to figure out the issue, start from the source and work your way to the motor. It has been a long time since i posted this thread, however, iirc there is a variable voltage that goes to the transistor for varible speed and a single wire that goes to the second relay for high speed that is independant. if it doesnt work at all.. start with the main power relay, and/or the logicon unit.

 

This writeup helped me a lot last year, altough my thermal fuse was the failure point(mounted under power transistor), not the transistor. I just had the failure a 2nd time and now know the problem.

One of the screws that attaches the leaf catcher grill(black grill at base of windshield) has a gasket that fails with age. The failed gasket leaks water into the HVAC system(the screw is directly above the fresh air intake), and into the blower motor. The water normally has no effect, but if it gets cold at night, the water feezes, locks the motor, and when you turn the motor on in the morning at 1/2 power setting, the thermal fuse gets really hot, because it gets no air flow, and fails. It's a cheap thermal fuse, but a pain to replace.

Thermal fuse replacement is from NTE electronics NTE8118. You need 15A and 121C opening themperature. I think the factory one was 118C.

 

A normal transistor doesn't have a resistance value (it's a junction, junctions are not supposed to but they do have a small amount of resistance). So how does a device that doesn't have a resistance value control speed?That's the job of a resistor, it's usually multiple in series. Transistor works like a relay when power is applied to the base, it allows power to go from the collector or the emitter, depends if it's an PNP or an NPN.

 

Sorry I meant resistors in parallel not series.

 

I just looked it up there's a blower motor resistor and a power transistor. The transistor supplies power to the motor and a relay after the resistor.

 

If a transistor is held halfway open, it can be used to control voltage. In that state it does have a large resistance and dumps the power it is diverting from the motor out as heat into the heatsink.

It might also be working more as a pulse width modulation, but I'm not sure where the heat comes from in that system.

I'm not an electrical engineer, but I think that's pretty much how it works.

 

sorry for resurecting this thread... anyone have the pictures?
they dont seem to work anymore and i really want to see this how to.

well actually i just saw that its a about a gen 2 rx7
i have an fd... :-P so no luck here