Manual fan control on t-stat not working, but Auto works...


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Old 12-28-12, 08:16 PM
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Manual fan control on t-stat not working, but Auto works...

I am having sort of an odd issue. My furnace blower turns on and off just fine with the t-stat fan switch in the auto position, but if I want to just turn the blower on manually it won't work. It has worked in the past but not anymore.

The reason I found out is because I was testing my new whole house humidifier. I have my humidifier hooked up to the EAC switch because I want it to run anytime the fan is not, not just when the heat is on.

Anyway, the weird thing is that when I put the fan switch in the on position I get power to the EAC as if the fan is on but the fan doesn't actually turn on. Also, with the fan switch in the ON position the blower still turns on and off normally as if it were in Auto mode.

So obviously the fan on signal is getting to the furnace since it turns on the EAC terminal. Why would the fan not start like it should?
 
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Old 12-28-12, 08:31 PM
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I was reading around and saw some stuff about low speed and high speed blowers. Someone mentioned that turning the fan on manually activates high speed. Is that true? and do all furnace blowers have 2 speeds?
I only have 4 wires going to the t-stat and the hot and cold blower terminals are jumpered. Would that mean I only have 1 speed?
 
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Old 12-28-12, 08:40 PM
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Does your system have AC (air cond) ?

A blower can be single, two or three speeds......depending on make and model.
Usually when the thermostat is in AC mode or FAN ON mode it's high blower speed.
When the furnace actually calls for heat thru the fan thermostat it's usually medium.
 
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Old 12-29-12, 10:47 AM
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Pictures are helpful. Make and model numbers of furnace and or thermostat helps. Also, what wire terminals in the thermostat are occupied?
 
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Old 12-29-12, 10:57 AM
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My heat pump unit worked that way (no manual fan operation). The AC guy said it was wired to start the fan after the heat came up and keep running until the heat dropped. He corrected the wiring in the outside unit so no delays. It now can be run via the T stat switch.
 
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Old 12-29-12, 11:00 AM
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Yes, it has AC. It is a Hunter thermostat like THIS one. There are four wires occupying W, RH (Jumpered to RC) G and Y/Y1.
I don't think it is the wiring because it has worked in the past.
Seems like something might be wrong with the high speed part of the blower? The furnace is a Comfortmaker RPJ II and the blower is a White-Rodgers Model 50A50 - 142
 
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Old 12-29-12, 11:05 AM
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Actually I guess the White-Rodgers part is just the control module.
 
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Old 12-29-12, 11:11 AM
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Jumper R to G at the thermostat. Does the fan turn on? If so, then it is the thermostat at fault. Jumper R to G at the furnace. Does the fan turn on? If so, then it is the thermostat or the wiring. If NO, then there is something wrong inside the furnace.
 
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Old 12-29-12, 11:55 AM
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Well it does not turn the blower on at either end but it does actvate the eac terminal which opens the solenoid for my humidifier. I do get a 24v reading across the two.
Is there something else i can try? It doesent even try humming. It did that a while back and replacing the capacitor fixed that.

One thing I do know is that the fan was in the on position for a long time at some point. Could that have burned something up?
 
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Old 12-29-12, 12:06 PM
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Do high and low speed actually have separate motors or to turn the fan does it just put a different amperage to it? It runs fine when the furnace calls for the fan.
 
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Old 12-29-12, 12:13 PM
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Only one blower motor. Could be one, two or three speed.

It has seperate wiring for the speeds.
 
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Old 12-29-12, 12:18 PM
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Alright, so the motor is probably fine if it works with the heat right? Is there a high speed fan relay or something that can be replaced or will I need to get a replacement board?
 
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Old 12-29-12, 02:28 PM
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It is likely your integrated furnace control board.
 
 

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