Electric Heat - Possible Wiring Issue

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Old 02-02-14, 09:24 PM
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Electric Heat - Possible Wiring Issue

Hi,

I have a Bryant A/C system with an electric heater built into the air handler, and I'm having a problem with the heat. I'm going to try to give all of the details of the problem, so sorry if this is a long post. I am in South Florida, so it's not urgent, but it would be nice to have the heat working whenever we might want to use it next.

First, about 1.5 years ago, the control board / delay board in the air handler blew in the middle of summer. At the time, I got a "lightly used" replacement board from a friend's husband that runs an A/C company. That board lasted about a month, then I had the friend's husband come out to fix it. He insisted on removing the control board and rewiring the unit without it, and I was desperate for A/C and didn't put up much of a fight.

We haven't tested the heat since then, but a couple weeks ago, when we tried to use it, it wouldn't work at all. The blower would come on during a heat call, but the heater would not. I tested that the thermostat was working properly by wiring the blower wire (G) to the heat call terminal (W), then setting the heat to on and turning up the set point. The blower came on, so I know that the thermostat was doing what it was supposed to.

So, as a next step, I tried using a jumper between R and W to get the heat to come on, and this didn't work. I opened up the air handler, and (after turning off the breaker) traced the wiring to see that one of the coil contacts on the relay was connected to the white wire, and the other one wasn't connected to anything. I found a common or ground cable off the transformer where one end of the blower relay coil contacts was connected, and I connected the second heat relay coil contact to this. After doing this and turning the breaker back on, I was able to get the heater to turn on by connecting a jumper between W and R; however, I still can't get the heat to work with the thermostat.

Any idea what the issue might be? I'm not sure if the thermostat is seeing some type of short when the relay is triggered. Someone also suggested that there could be a power issue that causes voltage to be read between the W and R wires, but that there's not enough power to trigger the relay via the thermostat. I think the transformer was replaced when everything was rewired, so this sounded plausible. I didn't want to replace it unless I'm more certain that this could be the issue. I appreciate any help or advice that you can offer.

Thank you!
 
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Old 02-03-14, 05:34 PM
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Sounds like you have a thermostat (or thermostat wire) problem.
Do you get heat if you jumper R, W, and G at the stat location?
 
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Old 02-04-14, 07:00 PM
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Thanks for the response. I tried jumping R, W, and G at the tstat and there was no heat. As soon as I removed the R-G jumper, the heat came on.

After trying that, I disconnected the G wire and turned the tstat on heat, and the heater came on right away. So, I then reconnected G and tested the voltage at the heat relay coil contacts when the thermostat was on a heat call with the blower on, and I was reading 0 volts.

Do you think that the transformer is weak or that there's a wiring issue that's directing all of the power to the blower during heat calls? Again, thanks for your help.
 
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Old 02-04-14, 07:22 PM
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Do you have a voltmeter at your disposal ? It could be real handy here.
 
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Old 02-04-14, 07:27 PM
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Yes, that's what I used to read 0 volts at the heat relay when the blower is on. The voltage at the output of the transformer is reading good. The problem only occurs when trying to call both the heater and the fan at the same time.
 
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Old 02-04-14, 07:36 PM
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It sounds like the white wire from the thermostat is not connected directly to the heat relay.
When you power the G wire it disables the W wire. Possibly the W wire is now connected thru the fan relay. Can you trace the white wire and see if anything is in its path ?

When R, G and W are connected you can check the transformer output but I'd guess it'll be normal.

When you jumpered R to W and the heat came on....... did the blower come on also ?
 
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Old 02-04-14, 08:37 PM
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I'll have to open up the air handler and double-check the wiring in there tomorrow. I don't think that the W wire is connected through the fan relay. When I jump R and W together, the heater will come on without the blower. I'll check the wiring more closely tomorrow and let you know what I find out. Thank you very much for the help.
 
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Old 02-04-14, 08:42 PM
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How do you know the heat is coming on ?
 
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Old 02-04-14, 08:46 PM
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With the cover off the air handler, I can see the heating coils glow through what I assume are some type of vent slots.
 
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Old 02-05-14, 08:02 AM
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You should call a different service company and have them install the correct control board for your unit.
 
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Old 02-06-14, 07:21 AM
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I took a closer look at the wiring and put together a rough schematic of how things are set up. I tried posting this last night, but it doesn't look like it showed up, so hopefully it works this time. There are also a few pictures, but they may not be too helpful because the wiring is pretty messy. If you have any other suggestions, I appreciate it. If not, then as suggested, I may try to have someone come out to re-wire a control board back into the system.

Rough Schematic:


Heat Relay:


Blower Relay with Transformer behind it:


Heat Relay with Heater Connections:


Complete Wiring:
 
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Old 02-06-14, 05:07 PM
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The relay would not run the fan in cool mode as you have drawn it.

I don't like that single pole single throw relay for your application. I would prefer a single pole double throw relay to operate more like the factory relay that is soldered to the control board. Whereas motor connects to relay Com, line voltage connects to normally open and the normally closed contact connects to the heating relay.
Motor common connects to the other leg of line voltage.



 
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Old 02-06-14, 09:01 PM
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I looked back at my drawing after reading your post, and I messed up. The ground on heating element #1 is correctly shown connected to the bottom of the heat relay; however, the ground for the blower relay and transformer should have been shown connected at the top of the relay giving them a direct connection to the ground from the breaker. Sorry about that. I'm going to blame the fact that it was late when I was drawing that last night.

Thanks for the advice. Rather than trying to modify the current setup to try to mimic the factory control board, I might try to get a new control board (plus a back up one) and re-wire one back into the system. Do you know of any good places to order them from? I have one of the ones that broke somewhere, so I can dig that up if there's any part number I should reference off of there.
 
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Old 02-06-14, 09:10 PM
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I am big fan of Amazon.
I have installed a couple of boards from that site. I get a lot of tools from them.
I am hesitant to give my credit card number to some unknown site.
 
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Old 02-06-14, 10:23 PM
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Amazon is basically a broker between you and another company. They have the clout to get the pricing and they'll help you if there's a problem with the order.
 
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Old 02-06-14, 10:33 PM
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Thanks! I'm a big fan of amazon and buy a lot from there. I can't believe that I didn't even think to look there for the control board. I really appreciate all of your help.
 
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