How can I test the 3 position ventilation fan switch in 87 S3 spider with a multimeter? Can't find anything on forums. Has four metal connectors on switch and three positions - Alfa Romeo Bulletin Board & Forums
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post #1 of 7 (permalink) Old 06-27-2017, 09:13 PM Thread Starter
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How can I test the 3 position ventilation fan switch in 87 S3 spider with a multimeter? Can't find anything on forums. Has four metal connectors on switch and three positions

I have it out and would like to make sure it works as I diagnose heater. Heater fan spins freely so that eliminates seizure of the fan.


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post #2 of 7 (permalink) Old 06-28-2017, 12:36 AM
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you say fan turns by hand freely, but does it also turn when you apply +12V direct one at a time to the yellow and yellow/black wires underneath the unit (to check both speeds)

and are these 4 wires all connected?

someone else will chime in about switch testing, but if it were me I'd just test trial and error.....its only 3 positions, one is off and two are on
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post #3 of 7 (permalink) Old 06-28-2017, 04:38 AM
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He's already dismantled the switch. See post:

http://www.alfabb.com/bb/forums/spid...ientation.html

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post #4 of 7 (permalink) Old 06-28-2017, 07:49 AM Thread Starter
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How do I test the switch with multimeter? I don't know which posts on the switch are power, ground, etc Do I use the resistance function on meter? Electrical is still a weak knowledge area sometimes.


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post #5 of 7 (permalink) Old 06-28-2017, 08:09 AM
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I've never dealt with that particular switch but there should be three wires: 1 for power, 1 for "low" and 1 for "high". There will be no ground on the switch - the switch only deals with "positive" power. The blower motor is grounded.

Yes, you would use the resistance function on your multimeter. You should see zero or close to it when the switch makes contact, infinity when not.

I don't know which is which on a disassembled switch but shouldn't be hard to figure out unless the switch is completely bad. One lead goes on the power, the other on one of the other two and toggle the switch. So just hook up the leads and toggle the switch. If you get nothing move one of the leads. There are only 3 possible combinations. At that point you should see a contact unless the switch is bad.

Do you have Papajam's electrical diagram? If not PM him and ask. Here's the switch on my '88 diagram. Pink is power, the two others to the blower motor. Obviously if it's in pieces it's not all that helpful.....:
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post #6 of 7 (permalink) Old 06-28-2017, 08:31 AM
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ah ok, thanks Brian...

Norcal, if the terminals behind are numbered (should be) then my 'guess' would be you put the toggle switch on so that the half with the Fan symbol sits on the side where terminal #1 is

kinda looks like that in Jim's wiring diagram snippet for an '88, here

EDIT: now that's weird, Chris got there first with an almost identical snippet!!
(mines bigger though, ha ha!)
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Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.

Last edited by spiderserie4; 06-28-2017 at 08:35 AM.
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post #7 of 7 (permalink) Old 06-28-2017, 01:43 PM Thread Starter
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Update. Cleaned inside of switch contacts with cleaner. Switch works! Theoretically it could be placed either way in housing, but easy to put it in, hook it up and then turn it around. Blower fan and system works as it should! That means, literally every button and switch and light works on the car. Not too shavby


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