TR fan control, new fuse, 2 new transistors

Here is the story...............

Heater fan only full on or off.

Replaced fuse as directed by Rifledriver and rotary control worked correctly for a day.
Replaced transitor and fuse again........fan remains full on or off.
Replaced with a second transistor and countless fuses........fan remains either full on or off.

Find it hard to believe I have many bad fuses and 2 non co-perative transistors.

Any ideas where to look next? Any help would be greatly appreciated.....
Thanks in advance.......Kerry

 

Bad connection for one of the above. Most likely to be where the terminal is crimped to the wire itself, not necessarily the connection between male/femal terminal contact areas.

 

Could be.............I'll check for continuity tomorrow.....thanks for the reply

 

I wondered this myself since mine craped out again....why can't the switch be replaced with a "pot" switch directly to the motor. Something you can get at Radio Shack for under $5.....

 

Nowhere did I tell you to replace it. It told you to check it in the first step of a diagnosis.

 

A pot generates too much heat to be located in the console. Manufacturers in the old days (I think a few still do) use a multi position speed switch shuttling power to a bank of resistors located somewhere under the hood where something that hot will not be a fire hazard. Otherwise a transistorized unit as the Ferrari has is used.

 

Excuse me.........I stand corrected.........Rifle driver said check the fuse, I did and "assumed" that if it were bad it would be a good idea to replace it.

Rifledriver..........a question, Did I do the "correct" move by replacing the blown fuse, or would you have advised otherwise? Christ, I gave you a thumbs up for giving me good information and still there seems to be a chip on a shoulder. Have a better day...............Kerry

 

When I told you that it was only a fact finding mission to find the cause. A blown fuse is an indicator of other problems in that system. So no, I was not intending for you to replace it right away.

On that occasion you chose not to listen, several times in fact. Fixing these cars provides me my livelihood and I freely give time and help those here who listen and do their part, quite a few times to people that are in this area and who otherwise might just bring their car here to be fixed. So in that way it not only costs valuable time it has also directly cost me money. It sometimes takes a great deal of my time and I will not waste it trying to help a person that does not hold up his end.

 

We must all tread lightly at times on this forum. It's a mix of many talents and occasionally a miscommunication will happen....but that's all it is. Kerry is one of the best, most stand-up people I've had the pleasure of meeting, and I'm happy to say I consider him a good friend. He is also one the the MOST RESOURCEFUL guys and can think outside the box and come up with alternatives I'd never thought possible. Rifledriver is beyond being called "extremely knowledgeable" and offers top-drawer advice and tips at no charge to all of us do-it-your-selfers. We blue-collar types have no reputation to uphold where-as guys like Brian are practically worshiped.....and rightfully so...do have to maintain a reputation and image. So any deviation from given advice is taken to heart. Let's keep things in perspective and see how Kerry's problem gets resolved. As you can tell I have a great admiration for both of these gentlemen

 

I thought this was a tech site.....not a therapy session to draw, quater and disect those who ask a simple question and hope to be greeted with an answer or at least some semblence of advice. Obviously you have a problem with me.............enough said. From this point forward I would hope that you might refrain from your profiling and just ignore any post that I may list in order to get some advice technically. This is a waste of forum space to air your opinions. It may be entertaining to you, but I am looking to talk with other fellow F-car owners about resolving problems......with F-cars, as well as being educated on how I can keep my car safe, comfortable, and roadworthy. I am not seeking ridicule, and taunts.............
Rifledriver, if need be send me a bill to cover your advice concerning my car and I will gladly send you a check, money order, paypal or if you accept Mastercard, I can settle my indebtness to you and then maybe we can move on. I am absolutely serious about "paying you off".....This is not sarcasim, nor frivilous.........Just wanna move on. Bill or invoice may be sent to Kerry Wittig, PO Box 629, Ithaca, New York 14851..............There I have done what I can to resolve this "situation"........

So with that out of the way.................

Anyone have any ideas as to what may be the gremlin in my HVAC fan control? As stated at the top of this thread I have replaced the fuse and voila' the rotary worked great, but then reverted back to full on or full off after a day. Replaced 2 transistors and a handfull of fuses............today I checked wiring and found no obvious culprit. The control may be the villian, but I find it odd that when I initially replaced the fuse it worked as designed.......I'm stumped!
Kerry

 

Hmmm.....so somehow something is creating the need for too much current and overheating things until the sacraficial "fuse" blows. If all the electrical connections seem good clean and tight, about the only thing left is perhaps the fan motor itself?

 

Yeah, but it works fine at full speed. So your saying that maybe when it is set to run at say half speed there is a problem? That is a thought.......maybe I can take another fan motor from another vehicle I have and see how that reacts.............Just hate paying $10 + for these sacrificial transistors.......LOL.......Good idea, I'll try that route. Kerry

 

You have a good point Kerry, you'd think at full speed the current draw would be at it's maximum as far as the fan motor goes and things work fine. What is it at partial throttle that could cause excessive current draw? Is there something that is bypassed at "full" running condition, but is in the loop at intermediate speeds? What else is in the circuit? If somebody knows please let us know as it seems this is a well known problem.

 

Yes, they are two distinct (and independent) modes of TR AC fan operation (even though there is only one control knob):

At the full speed setting -- a simple contact inside the switch ECU closes, which closes a relay, and runs the fan motor directly at the full motor current that flows at +12V (and the power transistor is completely out of the picture) and the current path is +12V-to-motor-to-relay-to-ground.

At anything less than full speed -- the not-simple electronics in the switch ECU controls the small current flowing in the base-to-emitter-to-ground path of the power transistor, and this small current in the base-to-emitter then determines (controls) the large current that flows in the +12V-to-motor-to-collector-to-emitter-to-ground current path.

The mistake in this design is that it doesn't match the usual common sense of 3/4 speed being easier on things than full speed. When you operate at 3/4~7/8 fan speed you are thermally stressing the snot out of the power transistor -- much better IMO to run at full speed and put the big current thru the relay rather than thru the power transistor (i.e., I use variable from 0~1/2 speed, but I jump to full speed if I want more).

The simplicity of the "full-speed" mode is why it is much more reliable.

Kerry -- Try reading-up/searching on "common emitter" on the web if you want to dig deeper into your variable speed problem.

 

Ah Ha..............that makes sense........Steve what modification(s) did you do and/or components were used to accomplish the 0-1/2-full if you could elaborate....Thanks, and I will do some more studing as you suggested, Kerry

 

It just dawned on me what may indeed be the problem..........

I have found a handful of problems with various electrical components in this TR.......All have been that wiring was either plugged into the wrong control or grounds not being present, etc.. I wonder if the transistor was "mis-wired from the get go? It appeared to have been replaced at some earlier time. what color wire goes where on the transistor. The colors are as follows:
Green with red stripe........was connected to the case.......C
Yellow...........................was connected to terminal.........E
Orange with red markings..was connected to terminal.........D

The pix below on the left is of the original packaging of one of the transistors I used. You can see that the diagram shows the connecting points and are labeled E, D, and C.

The pix to the right is of the "original" transistor I removed.........supposedly this is an item no longer available from RCA, as I was told by the vendor that I got the replacements from?!?!

Could this be "the" fly in the ointment?

Kerry
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I didn't make any modifications -- that's just how I manually operate the speed control knob.

It's such a hard thing to resist. My clothes dryer has a rotary temp setting knob, and I've noticed that it's just so natural to not set it at maximum, but to back it off a little (which I think is OK for my dryer, but not a TR fan).

With regard to the transistor itself, it seems the right kind of device -- a high-current, high power 3-terminal transistor (but that's your homework to figure out if a "drain" is a "base" ). Offhand the only thing still in my mind is that the (+12V) collector is connected to the case. I don't have your exact mid-US TR wiring diagram, but I'll check the wire color/usage on the others and see if it's consistent enough to make some guesses (of course, if someone's got the right TR wiring diagram book handy please speak up now).

 

Steve thanks for your explanation, along with taking the time and consideration concerning this issue.........

I picked up another transistor this morning.......But........I'm gonna wait to see if the wires were correct or not, before attempting to re-install. Hopefully someone out there in F land will have an answer..........

Kerry

 

Kerry -- No joy on the wire colors -- I forgot that they don't show the wire colors within the AC unit itself, but the functional connections are the same on all 3 TR schematics that I have:

With the key "on", the wire going to the collector should be +12V;

The wire connected to the emitter is connected ground when one of the AC round buttons is pushed on the early US TR and is always connected to ground on a late US TR (I don't know which type your mid-life US TR matches); and

The wire connected to the base terminal comes from the switch ECU and (on a working system) would be a small positive voltage (to make the small base-to-emitter current flow) that varied a small amount as you turned the knob when the AC system is "on".

 

Can someone do me a quick favour.....could you take a picture of the dash, and then where the transistor is located....ie through the side plate on the center tunnel or under the glove box....I may have to do this, but need where to look.

Also...is this something that since this problem can happen quite often, would it be smart to extend the wires from the fan to an easier location to replace the transistor?
Adam

 

I just had my fan quit on me all together. I check the 20amp fuse and the transistor and they are fine (swapped with functioning ones).

Fan doesn't run at any speed.

Any suggestions?

 

1. Check the connection in the "k" connector where the AC system gets its +12V power (two brown wires). If it looks like this, you've found the trouble

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2. If that connection seems OKish, measure the voltage on the two legs of the fuse while it is plugged in and when requesting the fan to run (obviously, you'll need to fabricate jumper wires to be able to measure this when the fuse is connected) -- if both are +12V relative to ground, the problem is downstream; if both are not +12V, the problem is upstream. (Doesn't say what the problem is but can help decide where to look next).

Good hunting!

 

Went to check this and lo and behold the fan was working?! I didn't do anything yet. It just decided to start working again.

Go figure.

Thanks for the advice.

 

Still wouldn't hurt to have a quick look at that connection in the "k" connector -- it's virtually free, it can be intermittent, and gets worse with time (even if it is quasi-working). If it is OK -- no harm done and no $ spent.

 

Any thoughts on fixing motor connection? After just returning from Ferr repair shop with fully working AC, the fan just stopped; fuses ok; left front AC fan (lt front of car) is running, compressor at engine comes on when switch is pushed on, but no AC air out of vents, so the blower under dash isn't running.
Any thoughts before I remove dash (horrors!)??
Thanks, thorn