Advice on a Carrier rooftop unit Gas Valves failing

RayWohlfarth

I am really confused on this. We have a customer with 7 Carrier model 48TCED16A rooftop units. The units are 8 years old and one has had the gas valve fail three times. We have checked the voltage and it is the same model and age as the other 6 I am kinda stumped what to tell the owner. When I talked with the distributor, their response was "Hmmm Thats weird."

GBart

What failed? the valve? the solenoid? Is it piped correctly? LP? NG?

RayWohlfarth

@GBart The main gas valve failed. We have power to it and it piped the same as what came from factory.The others are piped the same way Natural gas

GBart

Sounds weird, at 3 failures on the same unit the factory rep should be involved. They're going to want to know if it's a mechanical or electrical failure. Ohm one out and see if the coil is any good. There doesn't seem to be a tech bulletin on them. It's a long shot but I guess it's possible that there could be a loose connection causing hi amp draw that kills the coil but the odds are pretty high, unless there's debris in the line and it's ruining the valves mechanically.

Leonard

Might not be your problem , but.....
I had Carrier valve fail, old HVAC. Nat gas . City had low pressure main that rusted underground, groundwater dripped into main, evaporated, then condensed in winter inside cold $300 valve on roof. Corroded inside.

Water vapor also condensed inside gas meter and it froze up in winter , stopped delivering gas. Gas Co came out and put electric heat tape on meter. Was restaurant, used up to 900k BTU/hr nat gas.

Said if problem continued they could add methanol? bubbler to absorb moisture from the gas. I asked for it but they didn't want to add it unless more problems.

Not knowing any better I did it their way, valve didn't work next heating season. I should have sent them a bill.

JUGHNE

Thinking of what Leonard said is this unit the last one on the gas line or possibly not fired very often?

JUGHNE

As he said twice.

pecmsg

anything in the line?
What exactly failed?
End of the line or in the middle?

RayWohlfarth

@GBart The distributirs said they never heard about that before
@Leonard That happened to me weird Gas company fought with me until he saw pressure drop
@JUGHNE This takes care of south wing of tower. The building has three rooftop on each tower Got me scratchiung my head
@pecmsg gas valve looked like it did a years ago. Ready to get an exorcist

Leonard

More details please, would help.

How long did it take each valve to fail ......# months?

Did it fail during heating season, or at 1-st firing of new heating season?

What was failure mode ....... electrical open/short OR mechanical

wesPA

What was the incoming gas pressure? If each unit has a separate regulator ( like on a 2psi main) and that regulator is feeding the valve too much pressure, it can fail closed for safety. I had this happen sevaral times with rooftops.

SuperTech

I would definitely confirm that inet gas pressure is an important factor. Did you check the inlet pressure of all three rooftop units? I'm always suspicious of water and water vapour getting in the lines after reading stories about gas mains flooding.

Mike_Sheppard

I was called for a second opinion on a Lochinvar Armor once. Two of them and the gas valves kept failing. They had 2psi on the inlet with no regulators.

ratio

Amazing! I always check inlet pressure. In fact, if I had to check only one I'd check inlet before manifold.

Just replaced a pair of Trane negative pressure regulators because the plumber put 2# regulators on a 4# system & the diaphragm blew & put the full 4# on the gas valve. <smh>

unclejohn

That unit is missing something all the others have. Supply air sensor or board or somethin.

Leonard

Check that pressure reg's vent is clear and not plugged? ( mud wasp, ice from dripping water splash ....)
Might apply higher pressure to valve.

EBEBRATT-Ed

I am sure you have already checked this but I see tons of RTUs running on 208 volt systems where the multi tap control transformers are factory wired for 230 volt (as they always are from the factory) and the start-up guys never check this. You get down to about 106 on a 120 volt system or around 21 volts on a 24 volt system and your heading for trouble.

people slap there meters on and see the digits move or the needle swing (for old guys like me) and they thik it's good enough. Its not

SuperTech

It's quite common to see the wrong voltage selected on rooftop unit transformers, I've corrected numerous ones but I don't recall that being the main cause of trouble on any calls. I know a tech who doesn't even check his meter when measuring high voltage, if he hears the high voltage beep that his fieldpiece makes he calls it good. Drives me crazy, I'm an exact numbers type of guy.

clammy

Ray I think aside from chk voltages at transformer and line voltage I would throw a mana meter on the valve and chk incoming and manifold pressure . Recently did a start up where the gas line was undersized mention it to the installer he shrugged it off called tech service they agreed . He went increased the gas line re piped called me went to do the combustion testing and she was still off even though he redid the gas line I went to chk pressure and it was at 14 wc that’s was it for me made call to gas co n they replaced the faulty reducing regulator . I ve bad gas valves on roof tops but never 2 or 3 in a row some thing else where is afoul peace and good luck clammy

nicholas bonham-carter

Something definitely afoul!! What about a bad neutral or ground overloading the electrical part of the valve?—NBC

RayWohlfarth

Thanks for all the help. Sorry for not responding sooner I was laid up with a stomach bug

mikeg2015

Ice covering the vent on a regulator will cause it to stick open. Had 2 apartments fed by a common gas regulator (meters). One furnace kept running but was roaring. The other failed closed. If I pinched the shutoff down to 25% it would fire and run fine. Put het gauge on it and had to check it like 5 times as I wanted ot be sure before calling in the gas company.

Turns out there was a vent for the regulator that ran back inside the outside wall of the house up to the roof had comes loose and filled with water and froze.

There are filters for natural gas you could also try. Not sure but SOme might have separators with a peacock to drain them.


Otherwise, is there a aftermarket universal gas valve you could instead to rule that out?

Solid_Fuel_Man

The 208 and 230 voltage tap is so common. But one would think that you would see multiple units fail, not multiple valves on same unit.

They all burn the same gas, have same electrical supply. What's different?

Is this unit fed gas first?
Have it's own regulator?
Strange low voltage problems from bad XFMR or board?