blower fan speed stuck on high


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Old 05-08-21, 12:32 PM
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blower fan speed stuck on high

I've had this nagging issue for awhile. My old motor & board did this, and even after a blower motor swap and a control board swap (50A55-843) it is still doing this. My blower fan is a 3 speed and I'd ideally like the heater to blow on medium and the AC to blow on high. I have all the connections going to the right places. Do I need to alter wiring in the air handler, or is there something else I need to alter to get this to work? I'm stumped as to why it still does this after replacing those parts.
 
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Old 05-08-21, 12:49 PM
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Do I need to alter wiring in the air handler,
Did it work multispeed originally..... it's supposed to ?

A connection from R to W starts the heating process and after a time delay.... the blower starts on the selected heating speed.

A connection from R to G starts a short timer and then the blower comes on in high speed.
W/R 50a55-843 installation manual (pdf)
 
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Old 05-08-21, 02:04 PM
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No- the weird thing is it never worked originally. It was always on high whenever it was on. AC is fine, but on heat it moves too much air across the heat exchangers. Not that we need heat very much (Houston) but it'd be nice to get this working better.
 
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Old 05-08-21, 04:31 PM
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Ok.... a few questions.
When calling for heat or A/C...... does the fan run at the same speed ?
When calling for heat or A/C...... does the fan start in the same amount of time ?

Here's what the problem may be. On a call for heat the blower is delayed 45-90 seconds after the burner lights. The start up delay for the A/C is much shorter.

Your thermostat may be programmed to control the blower in heat and A/C mode. You don't want the t'stat controlling the blower in heat mode. You want it to be controlled by the board with the correct time delay and the heat speed.
Check into the system programming of your stat'. If you can't find it let us know what it is.
 
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Old 05-08-21, 09:14 PM
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When calling for heat or AC the fan runs at the same speed (high). And yes, the fan starts in the same amount of time whether it's AC or heat, which is pretty immediate.

Now in heat mode the blower and the draft inducer fans start at the same time which cannot be right. After about 1 minute the blower stops & starts with a bang in a split second. It's always on high speed here too.

As far as the T-stat, it was an old Honeywell replaced with an Ecobee 3 Lite. That didn't fix the fan speeds either. There also isn't a setting in the Ecobee to change this.

Everything at the board and thermostat seems to be wired correctly. Should I look for a crossed T-stat wire between the board and the thermostat inside the wall / attic ?
 
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Old 05-09-21, 05:58 AM
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In your original post you mention swapping in a motor and board. That board (50A55-843) has a diagnostic led and should have come with paperwork that includes a troubleshooting section. The ladder chart there includes areas to check if the blower is coming on improperly. If you have already checked this then obviously your a step ahead. If you are without the paperwork it's easily available online. Good luck.
 
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Old 05-09-21, 09:51 AM
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Fan control in Heat mode: Configures the furnace fan to be controlled by the ecobee3 or the HVAC system during heat cycles. Normally the HVAC system controls the fan during heat cycles.

On Thermostat:
1. Select Main Menu > Settings > Installation Settings > Equipment > Furnace.
2. Configure the settings as required.
 
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Old 05-10-21, 04:29 PM
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Thanks for that. I couldn't find those options (Lite version) so I did a software update and that made them show up. It worked to turn the blower on about 90 seconds after the inducer fan.

I'm not sure if it worked for the fan speed to go down to medium because my ears aren't that good, but I have a clamp meter I can use to test which connectors/wires are energized when the heater is running. Thanks again!
 
 

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