10 Ton Goodman RTU Gas Pressure Problem. - HVAC - Contractor Talk

10 Ton Goodman RTU Gas Pressure Problem.

 
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Old 01-01-2011, 06:19 PM   #1
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10 Ton Goodman RTU Gas Pressure Problem.


Hey guys I need a little help on this one. I installed a 10 ton RTU on a gas station here in Alabama in July. Winter time came and they fired up the heat, the unit ran no problem at first. Then they called me because of no heat, unit was not running. when I got there I checked the system out. The board was flashing a code 1. That code was for gas pressure, open limit, pressure switch, flame roll out etc... Every thing checked out. Checked gas pressure with a manometer. 7" wc Inlet. Dead on per specs. Outlet pressure is 3" wc. System calls for 5" wc minimum I tried to adjust pressures up. No go pressures will not rise. When I cut off gas and cut back on system will not fire up ( it was firing up even after lockout when breaker was cut of and back on) 3 tries lockout turn off breaker and back on tries 3 times, no go. After 10 or more tries system will fire up and run for about 60 sec. And poof off. Again outlet pressure is 3" wc. And won't adjust up. Only down. Anybody think it could possibly be the gas valve? This valve has a high fire and low fire adjustment on it. I'm not to familiar with this type of problem. Thanks for any help that may be available.
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Old 01-01-2011, 08:11 PM   #2
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


That should be 5" min supply pressure, not manifold pressure.

When you installed it, what were your low fire and high fire manifold pressures?

Isn't it suppose to start in low fire? If so, you will not get it up very high. And 3" is too high for low fire.

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Old 01-01-2011, 08:44 PM   #3
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


8 times out of ten, when system will only stay lit for a short spell, the culprit is dirty burners, dirty flame sensor, or some dust in the crossover channel (not sure if that's the correct term).

As B.T. said, you could have messed with the low fire side of the valve. Still, you should have a fire @ 3". Isn't one blink a fault code for open limit switch? I know that once I had a problem with a brand new furnace that would only stay lit briefly on low fire (Goodman). Upon further inspection, the blower fan speed tap on lo-heat was vacant, and the appropriate wire was placed on one of the park terminals...beware.
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Old 01-01-2011, 09:25 PM   #4
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Looks like Goodman says it should be 7 In/wc at the inlet at full fire, with manifold pressures of approximately 3.5 In/wc for high fire and 2.0 In/wc for low fire.
Is it possible the auto-reset limit in the blower housing is damaged or somehow open?
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Old 01-02-2011, 12:20 AM   #5
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Quote:
Originally Posted by DuMass
Looks like Goodman says it should be 7 In/wc at the inlet at full fire, with manifold pressures of approximately 3.5 In/wc for high fire and 2.0 In/wc for low fire.
Is it possible the auto-reset limit in the blower housing is damaged or somehow open?
Thanks guys. Of course it will be Monday before I go back out there. But I never checked the limit on the blower. But I also will get the gas co. Out because I only had 7" wc supply without the burners at full fire. So chances are there is not enough pressure there? What do you think?
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Old 01-02-2011, 05:25 AM   #6
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Before getting the gas company out. look to see what size the gas line is, how long it is, and then look to see if its large enough for the unit.
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Old 01-02-2011, 10:05 AM   #7
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Gas line is 1 1/4" from meter on ground up 15' of exterior wall, to roof. Then 25' to unit. Finally reducing down to 1" right before going into unit.also drip leg installed. This was a change out not new construction.
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Old 01-02-2011, 10:06 AM   #8
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Quote:
Originally Posted by hvactech140
Gas line is 1 1/4" from meter on ground up 15' of exterior wall, to roof. Then 25' to unit. Finally reducing down to 1" right before going into unit.also drip leg installed. This was a change out not new construction.
This is the only appliance on the gas meter.
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Old 01-02-2011, 11:26 AM   #9
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Quote:
Originally Posted by hvactech140 View Post
Thanks guys. Of course it will be Monday before I go back out there. But I never checked the limit on the blower. But I also will get the gas co. Out because I only had 7" wc supply without the burners at full fire. So chances are there is not enough pressure there? What do you think?
I think I'd get out there today. This sounds like a decent sized job, and there's no heat, it needs addressed asap. How many inches when the system was trying to ignite?

What I would focus on is the code. If one flash is a tripped limit switch, then figure out why it's overheating. The gas pressure is the least likely reason.
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Old 01-02-2011, 12:09 PM   #10
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Lol It's 65 degrees today in Alabama, so working on Sunday isn't really going to solve much. This store has dozens of portable coolers inside that puts off a great deal of heat. So they agree there fine till tomorrow. Here is the codes.

1 blink - ignition failure.
Open roll out switch
Open aux limit
Check -
Gas flow.
Gas pressure
Gas valve
Flame sensor
Flame rollout
Bad switch
Aux limit open

I have check everything, like I said I can't get it to fire now, so without it burning the wc pressures are 7" inlet. 3" manifold. With manometer hooked to manifold side and inducer running, the system tries to fire up but the manifold pressures are on zero, like the gas valve is not opening. There is 24 volt getting to the valve. After many attempts and lockouts. It will fire then the manifold pressure is 3" wc. But short after the flame just
"poofs" off. Then it's all the same again. I have sanded the flame sensor. Checked the pressure switch. Checked the limits etc. The only one I didn't check was the switch on the blower housing. The gas co. has been out " of course I wasn't there " but the had to change the regulator on the meter it's self. But they did get it adjusted to 7" wc not running. Thanks everyone for your responses, and when it's fixed I will post the find. But please keep the advise coming if possible.
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Old 01-02-2011, 02:04 PM   #11
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


If your firing at 3" in low fire. that will tend to open up the limits.

When you say 24 volts to the gas valve. Was that measuring across the valve. or measuring to a ground?
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Old 01-02-2011, 03:33 PM   #12
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Across the valve.
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Old 01-02-2011, 03:48 PM   #13
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Quote:
Originally Posted by hvactech140 View Post
Across the valve.
That would indicate a gas valve problem then, if your not getting gas out of the valve.
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Old 01-06-2011, 10:16 PM   #14
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


I got it guys, thanks. The roll out switc had a short on the board. Looks like straight out of the factory like that, but it's working great now. Just took a min to trace this one down.
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Old 01-08-2011, 10:31 AM   #15
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Re: 10 Ton Goodman RTU Gas Pressure Problem.


Quote:
Originally Posted by hvactech140 View Post
Lol It's 65 degrees today in Alabama, so working on Sunday isn't really going to solve much. This store has dozens of portable coolers inside that puts off a great deal of heat. So they agree there fine till tomorrow. Here is the codes.

1 blink - ignition failure.
Open roll out switch
Open aux limit
Check -
Gas flow.
Gas pressure
Gas valve
Flame sensor
Flame rollout
Bad switch
Aux limit open

I have check everything, like I said I can't get it to fire now, so without it burning the wc pressures are 7" inlet. 3" manifold. With manometer hooked to manifold side and inducer running, the system tries to fire up but the manifold pressures are on zero, like the gas valve is not opening. There is 24 volt getting to the valve. After many attempts and lockouts. It will fire then the manifold pressure is 3" wc. But short after the flame just
"poofs" off. Then it's all the same again. I have sanded the flame sensor. Checked the pressure switch. Checked the limits etc. The only one I didn't check was the switch on the blower housing. The gas co. has been out " of course I wasn't there " but the had to change the regulator on the meter it's self. But they did get it adjusted to 7" wc not running. Thanks everyone for your responses, and when it's fixed I will post the find. But please keep the advise coming if possible.
Sorry if I sounded all high and mighty. I was guilty of assuming it was cold everywhere. Good to hear that it was only a loose connection. Thanks for the follow-up, as it is always good to hear the outcome.

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