TR fan control, new fuse, 2 new transistors

Did you confirm that all blower fan speeds are not working? Or does full speed work, but nothing below full speed?

Also, I believe that the early TR fan speed control has the 1A replaceable fuse -- I'd try checking/replacing that before doing a dash-ectomy.

 

Steve, I tried the variable AC blower speed knob at all intervals, lowest to highest, but nothing happened...will look for fuse you mentioned - is it in the main fuse panel up front or a special location, like under the console? Many thanks, Thorn

 

Unfortunately, I don't have a picture, but this 1A fuse is on the speed control knob unit itself (so you have to get into the central tunnel). If you do, please take and post a picture

 

Where is the transistor located on a Mondial T?

 

Never mind I found it. Thanks anyway.

 

Hi All, been looking at the extensive history on these pesky blower fan issues with great interest. Thanks very much to everyone for making so much valuable info available (esp thanks Steve). Makes working on these vehicles so much less lonely.

I have a variation on this theme which I have not found a direct reference to in my searching. I have an 89 Testarossa in which the blower fan stays on all the time. A few days ago the fan was working normally (it is winter so it likely got a recent work out). Now the fan stays on full all the time - regardless of whether the fan rotary switch is off, low, 1/2, 3/4, high or full speed. I have removed the relay in the front clip for the time being to switch the fan off.

Before I start doing what Steve calls a dash-ectomy I would be grateful for any advice of where to focus in the search of this particular problem. Seem the symptom for the infamous resistor is for the blower to work only on full (and not for off or partial settings).
Many thanks and best wishes, Sean

which just question which I have not found car which has just started

 

That is a new (bad) one .

I'd suspect that the ...113 relay on the AC unit itself (that closes to run the AC cabin blower at full speed when full speed is requested) has failed/stuck in the closed condition. It's one of the three relays mounted to the AC unit -- one of the item 17 relays here:

http://www.ricambiamerica.com/parts_catalogs.php?M=FE&P=&V=diag&I=2927

IIRC, they are accessed via removing the panel on the LH side of the central tunnel. I'd try removing/replacing that relay as the first diagnostic step. Good Hunting!

 

Thanks Steve - sounds like a good place to start. Many thanks for all your help. Not sure what we would all do without your help and advice - particularly when it comes to the Elec-Trickery stuff. Take care. S

 

No trouble SBD. It's probably 50/50 whether the problem is with the relay itself or if the fan speed control knob assembly is (wrongly) always telling the relay to close, but either way you'll know by removing and then replacing the relay (while holding the outer case):

if upon reinsertion, relay doesn't "click", but fan runs full speed = probably a bad relay so just try another ...113 relay in that position (which you should do anyway since you're right there and sometimes the relay contacts can weld themselves together so there can still be a "click" even though the contacts are always closed).

if upon reinsertion, relay "clicks" (and fan runs full speed) = probably a bad switch inside the speed control knob assembly.

Another way to check this is to measure the voltage between the 85 and 86 female terminals in the relay socket after removing the relay -- should be:

AC off, or on, and fan speed set below maximum = 0V

AC on and fan speed set at maximum = 12V

Good Hunting!

 

Thanks Steve - been travelling so should be able to get to this in the next few days. Will let you know how I get on. Very good of you to help us all out as much as you do. Appreciated. Sean

 

Ok Back from a bit of travel and had a few minutes to have a look the pesky blower and this what I have found so far. Removed the relays you suggested Steve the basic 113 relays and they test fine. On the bench they click and switch. So then removed the other two - one is short and looks like a 113 (only 4 pin - one snipped off) and another which is much longer (also 4 pin).
The short one seems to bench test ok but I can't get the long one to do anything on the bench. Haven't had time to read up to see what this one does but with this relay removed the fan blower stays on as before.
I think I will look at the switch knob assembly next.
Might be able to borrow one of the long relays off another car to see if that makes a difference.
Horribly complex system - new found appreciation for Steve!!
Does anyone know how the "Long Relay" works or how to bench test it?
Best wishes, Sean

 

Your BDY29 is an NPN high power high current transistor. The case is connected to the collector. E obviously the emitter, and D the base. Are you using a Mylar or other insulator under the transistor to prevent shorts? Also many designs require heat conducting paste between the board insulator and insulator case. This allows the underlying area to be used as a heat sink. If not then one can be added if space allows. There are many designs to accomplish this. Also, many of these components are faked by China and others and are of very poor quality. Be sure to buy them from a reputable dealer. Mouser Electronics, Allied Electronics insure prime parts. There are substitute parts if you can't find one.

Replacement possibilities:

http://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=220&ucb=100&uce=75&ueb=7&ic=30&tj=200&ft=0.2&cc=0&hfe=15&caps=TO3

 

The "long relay" is a timer that occasionally engages the AC compressor when the windshield defroster lid is open and operating (to help dehumidify things even if asking for heat) -- no relationship to the cabin blower motor operation. (If you put +12V on terminal 30 and ground on terminal 86, occasionally terminal 87 will go to +12V, but you might have to wait a while).

Your post hits me as a little strange as you should have two ...113 relays and that one oddball relay with only 4 pins, but, if you remove all three of these relays at the same time, and the cabin blower fan still runs full speed = none of those are the problem.

If the power transistor has failed in a fully conducting state (emitter directly connected collector) or if the collector terminal was shorted to ground, the cabin blower would also run full speed -- so you might try inspecting that wiring and just disconnecting the power transistor and see if that stops the unrequested cabin blower operation.

 

Good suggestions Steve - thanks once again. Will do as you suggest next. I have so many projects on at the moment that I am tempted to just leave the main relay out. The flow through heating is fine so no real hardship.
Will let you know how I get on.
Thanks again and best wishes, Sean

 

Quick up date. No progress on the Black car with the blower motor that stays on - too many projects and travel. Got into the red car which had no fan at all. Found a blown fuse - but replacement blew instantly. Confirmed circuit board and white connector ok. Then progressive tracing of the two brown wires which in turn multiply at most subsequent connections (quite the cobweb). Split the wires at the white connector to confirm smaller of the two was the culprit. Dash-ectomy from there testing connections and relays as we went. Finally found that the barbarians that had installed a car alarm / stereo (many hers ago) had pulled on some OEM wires leading to the suction fan for the interior temp sensor (under LH or RH Dash behind small plastic vent) causing the two (non insulated) terminals to short. Very hard to find but all good now. I add this to the thread just in case it helps some ever suffering poor bastard in future. Best wishes Sean

 

Another brief up date. Progress on the Black car with the blower motor that stays on. Got into the red car which had no fan at all. Full dash-ectomy to tst all the relays - all tested fine but fan stayed on even with them removed. Found the 3 wire connector that leads to the Transistor (known trouble maker). When this connnector is unplugged the blower fan works on high only and not the lower speeds. This is consistent with Steve's observations of a failed Transistor. So looks like a new symptom for an old cause. Ordered a new transistor and will confirm when installed. Thanks again Steve - really help to get some guidence on this type of gremlin. Best wishes Sean