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Date:         Sun, 24 Oct 2010 15:17:44 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Is there a way to test the heater fan>
Comments: To: B Feddish <uprightbassghost@HOTMAIL.COM>
In-Reply-To:  <BAY113-W36E0337261588C6D0AC30ECE400@phx.gbl>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 02:02 PM 10/24/2010 -0400, B Feddish wrote: >The heater core is out. Besides the heater core leaking coolant, >there was tons of smoke last winter pouring out my dash one day when >the fan died. Lots of burning smells. Now I have a new fan motor too >but I do not see anything burnt in the heater box. Is it possible it >was that resister in there? It looks fine. Is there a way to test >this fan before putting it all back in today?

A good blower, in its housing but not mounted in the heater box, should draw about twelve amps directly from a well-charged battery and quietly deliver lots of air. That's an inconvenient number since common DVMs top out at ten amps, although the Harbor Freight one I mentioned recently goes to twenty.

*************** If you take three feet of #12 wire and clip your DVM (set on 200 mv range) leads 2' 6-1/4" apart on it*, you'll have an ammeter that will read four millivolts per amp at room temp. Twelve amps with this would be 48 mv. As the wire warms up it will read high, about two per cent for 10F. See http://www.reuk.co.uk/Make-a-Shunt-Resistor.htm for roll-your-own instructions.

* Ideally you'd solder leads on it that you could clip to, or leads with banana plugs that would fit your DVM. And the link above shows how to calibrate more closely if you care. ****************

Or wire the two in series to the battery -- do they run the same? Is the voltage drop across each the same? You could do this separately as well, but this lets you directly compare the operation of new and old motor.

Can you define "tons" of smoke, and can you characterize the smell? And what were the circumstances of the dying? What speed was the fan running at? If it was on high speed then the resistor is out as a candidate.

If it was on speed two and seized, the low effective resistance of the seized motor might cause the resistor to overheat and burn off any film of oil, leaf dust, fallout from that last snuff storm etc.

I think the motor itself is the best candidate. Does the varnish on the windings look burnt?

Now that you know how to do dashboards and heater boxes, would you like to come to Providence and do mine? :-)

Yours, David


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