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White Rogers contoller, model number 50A50-405 no voltage on terminals "C" & "Y"

White Rogers contoller, model number 50A50-405 no voltage on terminals "C" & "Y"


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Old 05-07-13, 03:18 PM
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White Rogers contoller, model number 50A50-405 no voltage on terminals "C" & "Y"

From another identical furnace that I have, there is supposed to be 24v AC
on these two terminals. The blinking light is steady. The fan runs when I have the thermostat call for AC - though the fan doesn't run as fast as the other identical furnace that is working properly.
 
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Old 05-07-13, 08:30 PM
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Welcome to the forums.

The C is common and the Y is AC active.

So you won't see any voltage on C and Y unless the thermostat is calling for AC.

A connection between RC and Y (such as when thermostat is calling for AC) would show 24vac on C and Y.
 
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Old 05-08-13, 04:56 AM
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Thanks for your reply.
Can I assume from your answer that when the thermostat calls for AC it shorts together RC and Y ? Does the controller also run the blower fan at a higher speed for AC than for heat? It seems that the blower fan in my second unit (I have two identical heat/AC units) runs much faster than the blower fan on the unit I am working on.
 
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Old 05-08-13, 10:04 AM
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The answers to your questions are yes and yes.

The blower motor speeds are selectable upon installation with the placement of the motor leads. Usually but not always... the AC fan speed is faster then heat.
 
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Old 05-09-13, 07:06 PM
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I found the majority of my problem. When I ran a wire between Y and R, simulating the thermostat calling for AC, I got 27 volts to Y and C which now sent voltage to the contactor in the outside unit. I found a bad connection in the thermostat wire where it was spliced overhead in the basement.
Since my AC background, such as it is, is from automotive, I tried to take the connector off the low pressure switch, to test it when I originally tried to find why the compressor wouldn't turn on, only to find out that there is no connector and that the leads are connected directly to the switch. When I bypass the switch the compressor turns on.
I feel that I damaged the low pressure switch and ordered another one. I realize that I may also have a low/no charge, but since I have no way to test the pressure and that fact that it is unlikely that there was low pressure and a bad thermostat wire I will replace the switch.
Thanks for your help
 
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Old 05-09-13, 09:19 PM
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If you didn't have a low or no freon problem you do now. The system would need to be empty to replace the pressure switch.

I would recommend enlisting the help of an HVAC company to replace that switch and recharge the system.
 
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Old 05-10-13, 01:21 AM
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I was given to understand that the switch sits on top of a Shrader valve as it does on cars. This valve should close when the switch is removed. Is this not correct?
 
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Old 05-10-13, 05:38 AM
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I can't confirm that. Maybe one of the pro's in HVAC can. They should stop thru.
 
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Old 05-10-13, 05:52 AM
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Thanks. I would appreciate hearing if there is a Schrader valve
 
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Old 05-11-13, 02:31 PM
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There may be a valve, there may not be a valve, you never know and this is why you should call a pro.
 
 

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