Heil Monster Furnace-Part 1


Old 02-09-03, 04:00 PM
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Heil Monster Furnace-Part 1

Thanks to you folks my propane furnace is runing great. Now I have a new challenge. My neice just moved into a townhouse with a Inter-City Product Corp (says Heil on the outside) NG hi-efficiency furnace. It gives two Model #'s, a Manufacturing # and a Serial # on the nameplate. One Model # is identical to the Manufacturing #:

Model/Manuf # NUG9075FGB1
Serial # L960769478
Model# GUM075N12A1

I have two questions and one big problem:

1. It has a disconnected vacuum line which tees into the burner enclosure and one side of vacuum switch. Other side of this switch is connected to inducer housing. It appears like this vacuum line should be connected to a barbed fitting on the gas
control valve, Honeywell SV9501M2726. Is this right? Also, why would someone disconnect this line? Is this an unsafe operating situation? Seems like gas valve is going to give wrong (high) manifold gas pressure because it is referencing against ambient pressure instead of enclosure vacuum.

2. Main blower on'ff delay can be controlled by three small togggle switches on the blower control board. Currently #1 switch is off and #2&3 are on which gives the factory setting of blower on 30 seconds after main burner ignition and off 140 secs after main burner down.
Old 02-09-03, 04:19 PM
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Heil Monster Furnace Part 2

2. (cont) Can anyone tell me how various on/off positions of those three switches affects blower on/off delay?

3. This furnace is a monster. No damper in supply duct and most air shoots directly to 2nd floor creating an inferno. Even so, still have lots of air to 1st floor. Reducing blower speed from med-high to low made little difference. Access to supply duct is very poor...can get to bottom only. I'm planning to fab a slide-gate type damper I can install from bottom to divert more flow to 1st floor. Stairs seem to act like a chimney so I'm afraid heat diverted downstairs will still end-up upstairs. Should I consider blocking downstairs return to force blower to recirculate accumulated 2nd floor hot air? House has 4 returns-one down and 3 up.

Should I consider reducing gas manifold pressure?

Main blower has 4 speed settings- does anyone know what rpms are associated with high, med-hi, med and low? Seems like I should have seen a bigger diference between med-hi and low.
Old 02-11-03, 11:28 AM
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What ever you do dont change the gas pressure. On the blower door or on the motor should give you the rpm of the motor.Id also say dont block the down stairs return till you see if just the upstairs returns would let the right amount of cfm back to the furnace ED
Old 02-11-03, 01:12 PM
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Thanks Ed. Poor choice of words on my part. I would only reduce gas pressure if it were too high.

Do you know the answer to my question about the Honeywell smart valve vacuum connection? My guess is the previous owner was having trouble with the inducer pressure switch not closing. Opening tubing up to room pressure makes it easier to close vac switch. Operating like this prevents ( I think) the vac switch from shutting furnace down if the inlet combustion air is blocked. Don't know how much it affects smart valve.

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