No 24V To Gas Valve - Cold - Please Help - HVAC - DIY Chatroom Home Improvement Forum

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Old 10-20-2007, 04:12 PM   #1
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No 24V to gas valve - Cold - Please help

I have an older Carrier 58ss that water from the collector leaked and
made its way to the blower control circuit board. We started having a
problem with the fan always being on so we called the company we have
service the furnace and AC come out. When the guy turned the furnace
on the blower control board shorted and started a fire(quickly
extinguished). I know I need to replace the furnace, but I have a cash floe problem right now.

The control board part was HH84AA005 is obsolete, the Carrier
replacement is HH84AA021. I also replaced the tranformer(scorched by
the flames) and the relay on the inducer board(corroded contacts from
the water dripping down). After installation, everything worked except
that there was no 24V to the Pick coil (terminal #3) of the gas valve.
While it is supposed to be a drop in replacement(if you believe the
docs), the board is significantly different with additional functions
and features. One big difference is that 10B1-2 that needs 24V can be
traced directly to the C terminal which goes straight to ground through
a plated mounting hole on the circuit board. There is no grounding on
the old board at all.

I have heard there is a service bullitin with modifications
required to make HH84AA021 work in a furnace that was shipped with a
HH84AA005? Does anyone know where I can get the information? Any other insights would be greatly appreciated.

Thank you very much,


boblu is offline   Reply With Quote
Old 10-20-2007, 09:50 PM   #2
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Call Carrier or a qualified service company. Cash flow or not this is NOT something you can play with.


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Old 10-21-2007, 12:19 AM   #3
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Still need help

Thank you for your comment, but actually it is within my skills to do the mods. I am an EE at a circuit board assembly plant. I have already contacted Carrier as well as local dealers and they refuse to share the contents of the service buletin. All anyone wants to do is sell me a new furnace.

If I can;t get any help here, then I'll have to create a schematic of the HH84AA021 board and figure it out myself.

Thanks again,

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Old 10-21-2007, 08:05 PM   #4
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Break down and call a service company. I've converted several of these furnaces to the new board but throw the service bulletin out back at the shop so I don't have one available now.

Go Buckeyes

Last edited by Buckeyetech; 10-21-2007 at 08:08 PM.
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Old 10-21-2007, 11:42 PM   #5
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Problem solved - the easy way

I was saved from having to reverse engineer the HH84AA021 schematic by a HH84AA005 board miraculously showing up on Ebay (what are the odds? ) This will get us through until I can afford a new furnace.

Anyone need a HH84AA021 board?

Thanks for the help!!


Go Ducks!!!!!!
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