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Help With Old Shop Heater

To: shop-talk@autox.team.net
Subject: Help With Old Shop Heater
From: Roger Waterhouse <rwaterhouse@shaw.ca>
Date: Tue, 28 Oct 2003 13:27:34 -0700
Hi;

I've been lurking here for a while and finally have something I hope you guys 
can help me with. It is now getting cold here in the Great White North 
(Calgary, Alberta Canada) and I need to get my garage heater working as I need 
to finish rebuilding the tranny in my Jeep. The heater is already installed 
(sorta) and is a Natural Gas Trane GPH-100K, this is one of those hanging 
warehouse unit heater devices and is 90,000 BTU so should keep me toasty. The 
PO totally screwed up the installation by mounting it too close to the walls 
and shoddily installing the combustion venting. I have rectified both of those 
problems, but when I turned it on prior to lighting the pilot, the fan came on 
immediately. I though that was a bit odd as in my admittedly limited experience 
with these heaters, the fan comes on at a preset temperature after the burner 
lights. After a bit of disassembly I found a defunct sensor (Thermodisk 11T) 
that had been bypassed and figured I had it beat. Went to get a replacement 
part and found out that the piece I had removed was a limit switch based on the 
170 marking. Yikes! The LIMIT switch was bypassed! So now I'm a bit stuck as 
there are two things I cannot figure out, and cannot seem to find any 
information or help on.

1. This limit switch has 3 connectors, so there are two switches, one normally 
open and one normally closed. The normally closed one is obviously intended to 
be used as a limit, what the heck is the other for? It had a wire on it, but 
had been disconnected in the junction box.

2. Where is the fan control? There are no other sensors. Is the fan REALLY 
supposed to be on all the time?

The only ideas I have come up with are that either the fan is supposed to be on 
all the time, or the limit is also a fan controller. That doesn't seem very 
workable as the fan would come on at exactly the same time the limit trips and 
cuts off the gas.

Any ideas or suggestions welcome.

Cheers
Roger





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