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Old 02-16-2012, 07:06 AM   #16
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Residential Furnace relay module sparking


Warmer weather this weekend. I am going to check the connections to the board. If all looks good, then I am going to replace the 20 yr old thermostat. If I still have a problem, then there could be a bad component at the heat pump condensor sending the signal back to the board.

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Old 02-20-2012, 09:46 AM   #17
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Residential Furnace relay module sparking


I replaced the thermostat this weekend and everything seems to be working fine. The new thermostat confirmed that the chattering occurs when you increase the temperature and "Aux heat" kicks on. During Aux Heat, the relay still starts to chatter. I looked at all the soldered connections to the board and they all looked good. I put a little pressure on the relay and the connection seems firm. So it looks like either the relay is bad or a connection is bad.
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Old 02-20-2012, 11:09 AM   #18
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Residential Furnace relay module sparking


I'm thinking that relay coil runs off of your 24 VAC transformer that also powers your indoor and outdoor units. When the aux heat kicks in, the extra load could be lowering the 24 volts enough to cause the relay to chatter. It could be a faulty contactor, weak 24 volt transformer, loose connection, lower than normal 120 volt input to the transformer, etc, etc.

Before replacing the relay I would measure the coil voltage when it is operating properly and when it's chattering, noting the difference.
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Old 02-20-2012, 04:40 PM   #19
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Residential Furnace relay module sparking


I replaced the transformer a couple of years ago. Also changed out a contactor relay next to the transformer at that time. I also added a 2amp in-line fuse at the transformer for added protection. This all seems to be working fine. I checked the voltage at the thermostat and had ~25 amps. This confirms the transformer is working. I will probably check the voltage at the board and see what changes during aux heat mode. All connections I have looked at so far look good. Thanks for the help. I might be getting closer to the problem.
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Old 02-27-2012, 07:23 AM   #20
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Residential Furnace relay module sparking


I meant to say ~ 25 volts (above)... Anyway this weekend, ran heat and I noticed that while in "aux" heat mode, the heat pump (condensor) tries to run but kicks off. It comes on and runs for a few seconds and shuts off. This all occurs while the heat is running (blower fan is runnig with hot hair coming out of registers) and the relay at the board is clicking. It is almost like the relay can't handle both the heat pump and gas furnance mode running at the same time.
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Old 02-27-2012, 07:40 AM   #21
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Residential Furnace relay module sparking


Or the heat pump is low on gas and cycling off because of a low pressure sensor switch.

This sounds like a backwards setup. Normally a heat pump would be the first stage of heat and the electric or gas would be the backup second stage.
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Old 02-27-2012, 12:33 PM   #22
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Residential Furnace relay module sparking


The heat pump runs normally in heat mode. When you turn up the thermostat up enough, it kicks in auxillary heat mode, this is when the furnace comes on. While in aux heat mode, the relay chatters and heat pump seems to shut off and try to come on. At least this is what I observed the last go round. I probably need to verify this.
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Old 02-27-2012, 02:21 PM   #23
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Residential Furnace relay module sparking


Can you measure the transformer voltage. Sounds like the control voltage transformer might too small and dropping voltage when both stages are on. What is the make and model of the unit?
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Old 02-27-2012, 07:23 PM   #24
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Residential Furnace relay module sparking


Quote:
Originally Posted by bupa94 View Post
The heat pump runs normally in heat mode. When you turn up the thermostat up enough, it kicks in auxillary heat mode, this is when the furnace comes on. While in aux heat mode, the relay chatters and heat pump seems to shut off and try to come on. At least this is what I observed the last go round. I probably need to verify this.
I am thinking the transfomer is too small or something is shorted on gaz furnace side.


Quote:
Originally Posted by joed View Post
Can you measure the transformer voltage. Sounds like the control voltage transformer might too small and dropping voltage when both stages are on. What is the make and model of the unit?
I am with Joed with this one and once you posted the model number we can able figure it out.

Bupa94.,

Did the gaz furance did work ok when you shut the heat pump down ?

If not there is a issue with connection either the control board or gaz furnce is not hook up properly.

By the way how many conductor you have in the thermosat cable ??

Merci,
Marc
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Old 02-28-2012, 12:51 PM   #25
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Residential Furnace relay module sparking


I have not measured the transformer voltage yet. The transformer is only a couple of years old. From memory there are 5 or 6 wires coming from the theromostat. I think it is the typical set up for Lennox Heat pumps. I will have to check my notes later.

1 - 24v
2 - common ground
3 - heat
4 - reversing valve
5 - blower
6 - compressor

Here are the specs for the furnace:

GAS FIRED FURNACE
MODEL #GS18Q3-75-7


Circut board: OKC-1 A Heatcraft
OKFUELMASTER 58851

Relay: AROMAT AP334298K
HC4-HP-AC24V

HEAT PUMP
Lennox Model # HP20-411.

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