View Full Version : trane rooftop
03-10-2005, 10:10 PM
I got a ccall today and as luck would have it (and many layoffs) i was the only tech still on the clock and everyone elses phones were off.
The call was a complaint about smelling gas right after start up.
so up i go to the roof. The unit was a trane. With a huge single burner that reminded me of a mobile home furnace. And right below the gas valve and inducer fan area was a 3/8 copper tube coming out of the heat exchanger.
I've never seen this before. There was a rubber tube stuck on it leading out of the chamber through a hole to fresh air. The tube was dry rotted and crumbling apart and basically venting out (?) into the compartment.
So what was it?
Being that it looked like it needed a tube there i swagged 3/8 copper and fit it over the tube and ran it out side of the unit.
03-10-2005, 10:18 PM
It's to drain accumulated moisture out of the heat exchanger to prolong it's life. Do a search on here for a Trane burner book. Someone had posted a link to a site that had the book which explains the negative pressure gas valve and it has heat exchanger info as well.
03-10-2005, 10:49 PM
My shop has a problem with training also. Don't break out the jumper wires until you learn more about this equipment. If you have the specs you would find out the unit is variable DC control circuitry, next you would find that you have negative pressure st the gas valve.
03-10-2005, 11:16 PM
i have seen on those units that the gas smell comes from when there is a just the right wind and the gas valve is not set just right the unit would go to light and miss fire the first time but light the secound time but after the first miss the gas in the chamber is being purged out by the venter motor and the fresh air intake is sucking in the gas. or check your heat exchanger for a crack
03-11-2005, 06:14 AM
northern boy. That sounds about right. The wind has been kickin mad out here lately.
i spent some quallity time stuck in the cabinet looking at the heat exchanger. Couldn't find any problems.
i read on the gas valve that it was negative pressure -.02 wc I've never seen that before either.
thanks for the info.
03-11-2005, 06:53 AM
The gas valve is called a negative pressure valve because it takes a negative pressure to open it,not because it runs at -.2, the -.2 comes from the delta P, of the combustion blower it sucks a vacuum at the valve outlet at - 3.7 and the valve is set at +3.5 the difference is the -.2
[Edited by fat eddy on 03-11-2005 at 06:56 AM]
03-11-2005, 06:12 PM
Had a similar problem with a Voyager unit. Frequent complaints of gas odors. This went on for a year. Checked all the obvious, like economizers etc. Fimally caught the unit mis-firing but wasn't sure how smell was getting in building. Found several loose screws around front plate of heat ex. and more around rear plate. Also found gas manifold somewhat askew where it went into the blower plate. Tightened all screws, adjusted gas line and set up pressures alla the "Burner Book" and havent heard from the customer since.
This building has 11 units and the odor was always thought to have come from a different unit so the Voyager was not looked at up until this point.
03-11-2005, 09:36 PM
Timmmayyyy.....I just love saying that!
03-13-2005, 05:45 PM
Sounds like ( as others have hit on) raw gas is being ex-
hausted (due to failed ignition trial) and being drawn in
somewhere like fresh air intake of that unit or another unit
03-16-2005, 11:18 PM
Ahh.....the mysterious gas smell in the space from a rooftop gaspack. The unit never misfires, the pressures are perfect, 500 screws later, the top and side panels are off, and you can't find any holes or cracks with your 10 inch retractable mirror. Been there, done that.
Save yourself a lot of time with these four things.....a reversable shop vac, a small piece of metal, some cardboard and some ductape. Everyone know what I'm saying? Note: Make sure the heat exchanger is good and hot when you do it ;)
03-21-2005, 10:05 PM
I'm with the others. I've found units misfiring or not firing at all while trying to light and the wind picks up the raw gas and either the same unit or another unit on the roof picks it up thru the fresh air.
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