Neither A/c nor furnace would turn on; Fan runs continuously

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Old 05-14-18, 06:56 AM
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Neither A/c nor furnace would turn on; Fan runs continuously

I have an Amana HVAC unit. The label on the back of the unit says - Goodman Company Model No. CAPF3636B6AA. It was installed in 2007.

Today, attempting to switch on the A/c for the first time this season, it wouldn't turn on. Noticed that the internal fan runs continuously (did make sure that the thermostat is on AUTO).

On further investigation, I found that the furnace wouldn't switch on either if I switched the thermostat to HEAT and increased the temperature.

Thermostat does click as expected. I tried switching off the unit using the main switch on the unit and switching on after a while.

What could be the issue? Appreciate the help. I would like to try and fix it myself if possible.
 

Last edited by do_will; 05-14-18 at 08:11 AM.
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Old 05-14-18, 09:11 AM
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Try and run the ac and heat, while checking for a call at the low voltage terminal strip.
 
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Old 05-14-18, 07:32 PM
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Is that the voltage between G and W on the control board?
- Lowered the temperature on the thermostat to below room temperature (Did hear the click)
- Voltage between G and W is around 0.

Is that bad?
 
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Old 05-14-18, 07:34 PM
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G is the blower.
W is the heat.
Y is the cooling.
R is the power.
C is common.

Check between R and W
And R and Y
 
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Old 05-14-18, 08:19 PM
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A little confusion here. That's not a furnace model number. Looks like a cooling coil number.

If this is a gas furnace.... we need the model number posted inside on the side wall near the burner.

It sounds like there is an open limit switch. Check for 24vac from R to C.
 
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Old 05-15-18, 06:08 AM
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Sorry about the confusion. The model number is AMH950703BXAC.
The control board is PCB00109.

I checked some voltages. They are all zero - R to C, G to C, W to C (With thermostat set for heating).

Thermostat seems to be doing its job. Checked continuity on switching to heat. Seems fine.


Noticed that the fault LED is flashing on the board. Looking at the manual, it says "Open RO Switch". The switches (2 of them) bellow the burner look closed (Small button in the middle are pressed in). Tried to clear the fault using the fault recall button for a long time. Didn't work.

Thanks for all the help. This is a learning experience for me.
 
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Old 05-15-18, 06:12 AM
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Test the rollout switches to see if they are open.
 
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Old 05-15-18, 06:31 AM
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Checked continuity on the RO switches. They seem closed (has continuity)
There is another switch below the RO switches. That has continuity too.
See in the image below (all circled in yellow)

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Last edited by do_will; 05-15-18 at 09:08 AM.
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Old 05-15-18, 10:25 AM
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Made sure that the RO switch circuit and High Limit switch circuit are closed and the Pressure Switch circuit is open (all as expected).

Is it safe to assume that the board is bad ?
Could that fault code be the reason there is no voltage between R and C ?

I am tempted to just buy a new board and try it on.
 

Last edited by do_will; 05-15-18 at 10:42 AM.
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Old 05-15-18, 02:00 PM
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Just found out that six flashes also means that the fuse may be blown. And, it was ! Going to replace the fuse.

I wrongly assumed that, since the LED was working, fuse can't be an issue.
 
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Old 05-21-18, 10:42 AM
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Just an update - Replaced the fuse. That too blew immediately on running AC. Furnace runs fine. Checked wires to outside unit for short. Disconnected it from contactor - System runs fine without blowing fuse. Only part left to check is the contactor. Just ordered replacement. Will update.

Anybody thinks it could be anything other than the contactor ?
 
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Old 05-21-18, 07:14 PM
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It's more common for the wiring between the house and the condenser to have a problem but if you disconnected the contactor and the short was gone..... it would appear the contactor has a shorted coil.
 
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Old 05-22-18, 11:06 AM
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SUCCESS !! The new contactor did the trick. The low voltage terminals on the old contactor were shorted.

Thank you for the help ! Big thanks to PJMax. You had helped me when I had defrost issues with the refrigerator too.
 
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