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Old 01-06-2009, 05:37 PM   #1
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Heil Help!


Newby here.

We replaced a 12 year old Day-Night central a/c Furnace that was having problems with the a/c compressor losing charge. Contractor could not find a leak, so it appeared it was in the lines that are buried in the concrete slab of the garage floor. As it did have some years on it, replacement seemed prudent. The contractor replaced the furnace, A/C, and connecting lines with a Heil unit in summer of 2008. At the time the heat in the SoCal desert was so high he couldn't test the furnace operation and the A/C worked fine. Now this winter, the furnace has never worked. The ignitor and purge fan come on, but the gas valve never opens. The ignition sequence keeps repeating and does not stop after 3 tries as it is supposed to. The green fashing LED is indicating no problems. The valve will open if power is supplied directly from the transformer. So, I assume it is not the valve or the transformer. Contractor has changed the circuit board, no joy. Heil told him it was a bad ground. We have re-grounded everything and problem still exists. It appears to me that there is a bad sensor somewhere. He is trying again this week to contact Heil.

Any suggestions appreciated.

Edited to correct date. 2008 was year when it was installed.


Last edited by PHOnos; 01-06-2009 at 09:29 PM.
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Old 01-06-2009, 06:45 PM   #2
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May be a wiring issue in the gas valve circuit. Maybe a defective spill switch. Do you have a model and serial number.

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Old 01-06-2009, 08:32 PM   #3
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Originally Posted by SKIP4661 View Post
May be a wiring issue in the gas valve circuit. Maybe a defective spill switch. Do you have a model and serial number.
I'll have to get it this weekend, out of town (where it's a little warmer) on the coast this week.

Thanks for the reply, Skip.
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Old 01-06-2009, 08:38 PM   #4
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Does the ignitor glow.
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Old 01-06-2009, 09:03 PM   #5
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Does the ignitor glow.
Yes, it does.
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Old 01-09-2009, 08:29 AM   #6
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This is probably a silly question, but did the contractor at least fire the furnace up to make sure it fired up and ran? If not, could it be air left in the lines? Is the supply gas valve open? Silly questions, but sometimes if a unit can't be fired up to check it out, the contractor will suggest a return visit to bleed the lines and finish checking it out and plan on firing it up then?
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Old 01-19-2009, 10:17 PM   #7
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Ok, everything above has been tried to no avail.

Limit switches have all been jumpered, no joy.

The contractor set up a conference call with Heil in Tennesee and the local contractor. Now waiting for a new wiring harness.

Here's the wierd one -- the voltage on the wire to the gas valve coil goes to 24 volts when unconnected to the valve and heat is called for, but drops to 0 volts when it is connected to the valve. The valve will open if 24 volts are applied directly from the transformer.

Could it be there is a partial open or non-direct short in the valve coil itself that some circuit on the circuit board (or the CPU) recognizes and drops the voltage without triggering a fault code on the board?
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Old 01-20-2009, 08:51 AM   #8
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I think it would probably be a bad relay on the ignition board.
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Old 01-20-2009, 01:12 PM   #9
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is this an n9mpv ?
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Old 01-20-2009, 03:40 PM   #10
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Sounds like a bad connection at a molex plug. Trace both wires from the gas valve backwards and at each connector check that when the plug was pushed together the wire did not move out of position. Or use a electric meter and do the same thing using tools.
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Old 01-21-2009, 10:03 AM   #11
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Originally Posted by SKIP4661 View Post
I think it would probably be a bad relay on the ignition board.
That was our first thought, but the board was changed out.

Thanks, SKIP.

P.S I suppose both boards could be bad. I've seen this in solid state relays in a gas dryer.

Last edited by PHOnos; 01-21-2009 at 10:07 AM.
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Old 01-21-2009, 10:15 AM   #12
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is this an n9mpv ?
Thanks for your question, Dr Heat. Is this the furnace, gas valve, or <?> model number?

Someone asked for information before but I forgot to get it when I was in the desert. Now back on the coast. Have to get the literature when down there again.

-P
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Old 01-21-2009, 10:19 AM   #13
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Originally Posted by JohnH1 View Post
Sounds like a bad connection at a molex plug. Trace both wires from the gas valve backwards and at each connector check that when the plug was pushed together the wire did not move out of position. Or use a electric meter and do the same thing using tools.
Thought about this too. I guess the rep at Heil did also. This is the reason we are awaiting a complete new wiring harness assembly.

Thanks, JohnH.

-P
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Old 01-21-2009, 10:31 AM   #14
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try running common all the way back to the transformer sounds like your loseing it somewhere
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Old 01-21-2009, 07:40 PM   #15
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Quote:
Originally Posted by PHOnos View Post
Thanks for your question, Dr Heat. Is this the furnace, gas valve, or <?> model number?

Someone asked for information before but I forgot to get it when I was in the desert. Now back on the coast. Have to get the literature when down there again.

-P
N9mpd (not v my bad) is a furnace model number

Maybe you can answer this is the blinking light on the board or the gas valve or both?

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