Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

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Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Oscar Redding » Tue May 26, 2009 11:48 pm

I have a Nordyne MGHA-056ABFC-05 furnace. I am having to replace
the control and relay switch box with 2 wire a/c control box 901994 which I just received from Aberdeen. I will have to make some wiring changes because of some minor differences. For one, there is a 24v transformer in the furnace section which I understand will have to be disconnected. This will eliminate some wires going to the control box. This will leave me with a red/white and black wires that should be connected to power in. and 2 smaller wires that wire in the heating such as the gas valve and limit switches. The blower section should plug right in. I guess my question is that if I treat this new control box as a self-contained unit that if I connect up the external wiring such as the power and the two heating wires and the 4 thermostat wires and blower plug that the unit should be fully functional. Am I on the right track? Thanks much. Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Thu May 28, 2009 3:20 am

Hi Oscar,


IF you have 4 t-stat wires, you do not need a 2 wire a/c control box, you'll need a 4 wire a/c control box.


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Postby Oscar Redding » Mon Jun 01, 2009 11:46 am

Please help. I knocked out the transformer on the ac 901994 . I'm not good at explaining but will try. My new control boc seems to match uo with the old one in the following ways. It has the same letters on the terminal block that is CYWR, the old one is YRCW. I connected up the condenser wires to YC and the furnace wires to RW. I connected the blower to top of control box and the High voltage terminal block to furnace box and the red low voltagew wire to the red wire from aux limit switch and the white wire from the gas valve. I am unsure about the red, white and black power leads as the red lead does not have a red power lead. Please advise. Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Mon Jun 01, 2009 5:05 pm

How many wires are connected to your thermostat ?


You stated earlier that it was 4. If so, you have the wrong a/c control box as stated in my previous reply.



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Postby Oscar Redding » Mon Jun 01, 2009 7:26 pm

I'm sorry for the confusion. There are only 2 wires coming from the thermostat. There are two more wires but they ae coming from the contactor on the condensing unit. Thanks, Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Tue Jun 02, 2009 1:39 am

Hi Oscar,

Two condenser wires go to C and Y

Red from t-stat goes to R

White from t-stat goes to W


Blower plug goes to a/c control box top plug.

Bottom of a/c control box plug (white-black-red) goes to furnace control box top plug.


Red wire from bottom of a/c control box wire nutted to red wire from top of furnace control box.

White wire from bottom of a/c control box wire nutted to white wire from top of furnace control box.



Nothing else should have been disconnected and this should complete the wiring for new 2 wire a/c control box.



Thanks,
Robert
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Postby Oscar Redding » Tue Jun 02, 2009 2:54 am

Hi, I need to replace the 24v transformer I burned out in the new control box, can you give me a part number? Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Tue Jun 02, 2009 4:27 am

Hi Oscar,

Transformer # 621098 .



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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Oscar Redding » Sun Sep 20, 2009 12:12 am

Hello Robert, I followed your instructions for replacing control box. I ended up with the ac working but thermostat would not,. I used the ac but now need the furnace, but it is not working. I turned off the AC circuit breaker and switched over to the furnace. I found a broken connection in thermostat and repaired. I turned up thermostat and switched on the heat/Cool switch to heat but gas valve does not come on. Could you advise me what to check for? Thanks. Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Sun Sep 20, 2009 7:55 pm

Hi Oscar,

See if you have 24-28vac across W and C at a/c control box terminal board on top WITH t-stat temp lever set at temp higher than room temp.


Be sure switches on front of control box are set to Heat and Auto.


IF your t-stat has switches, set them to heat and Auto also.




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Robert
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Oscar Redding » Mon Sep 21, 2009 8:37 am

Dear Robert, I have no switches on t-stat. I set control switches to fan auto and heat. I AM getting 24v at W and C. with lever on t-stat calling for heat. Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Oscar Redding » Mon Sep 21, 2009 11:32 am

Dear Robert,I have 24 volts from W to C with lever set to heating. Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Mon Sep 21, 2009 7:01 pm

Test at gas valve for 24vac .



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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Oscar Redding » Mon Sep 21, 2009 9:24 pm

Robert, There is NO voltage at gas valve. Oscar
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RE: Nordyne MGHA- 056ABFC-05 with 901994 relay switch box

Postby Robert » Mon Sep 21, 2009 10:22 pm

Hi Oscar,

Then you will have to remove the front covers from both control boxes.

Then look on underside of W and follow the wire, testing at to ground for 24vac at each component or junction with another wire to find where the 24vac low voltage is lost.


May be time for an hvac tech to find the problem.



Thanks,
Robert
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