# A/C Fan Speed won't click to High



## SeattleIS300 (Jul 10, 2010)

Not sure if anyone can help me here.

I have a Bryant 350MAV furnance and a Rheem A/C unit/Coil. What is occuring is I can't get the fan to switch from fan speed to High when I use the Cool setting on the stat.

Backround Info.

We had the blower motor replaced 2 months ago and it appears to be working fine. I also had a tech come look they told me the control board was bad. I purchased one and replaced it same issue.

We don't get any HIGH Airflow just the standard FAN airflow when we switch from Fan to Cool. This reduced airflow is freezing our A/C Coil and reducing our cooling.

What could it be? 

Thanks,
Joe


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## lloyd (Jul 11, 2010)

Did you have this problem in the time leading up to the first blower going bad? It could be that the tech that replaced your blower either used a blower motor of lesser speeds or didn't hook up the high speed. Some blowers have 3 or 4 speeds. high, med, low,  or..... high, med high, med low, and low.

Also if your unit is low on refrigerant it can cause icing. Dirty evap coil and or filter can cause icing.


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## Wuzzat? (Jul 11, 2010)

Yes, look on the schematic for how many speed taps are on your motor.
Could be both control boards were fried by the yet-to-be-found root cause.


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## SeattleIS300 (Jul 11, 2010)

I don't know if I had it lead up to or not. We were in Winter and not running the A/C at the time. I checked the blower motor speed and it was the same as the one that was taken out etc. I'm not sure about the speeds but I checked the colors and red, black and blue all went to the correct spots.


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## SeattleIS300 (Jul 11, 2010)

I'm thinking the old motor was a 4 sp and the new is a 3sp but the HIGH Should be the same speed if they are both 1075RPM correct?


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## lloyd (Jul 11, 2010)

> I'm thinking the old motor was a 4 sp and the new is a 3sp but the HIGH Should be the same speed if they are both 1075RPM correct?



Right on this. Wonder if the run cap was replaced? (usually clamped to the outside of the blower housing)
You can pick up a run capacitor for a few dollars and hook it up, just two wires.

Like Wuzz was saying you may have a fan relay on your board could be bad. In my experience, fan relays tend to be chincy on alot of these control boards.

But even if you have decent air flow, you shouldn't be freezing up. I'd have the charge checked or check it yourself if you can. You can buy your own guages for less than the price of a service call. If you have 60-70 psi on the suction side you're ok.

lloyd


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## Wuzzat? (Jul 12, 2010)

lloyd said:


> you may have a fan relay on your board could be bad. In my experience, fan relays tend to be chincy on alot of these control boards.


At rated current, less than 30 mV across closed relay contacts is good, more than 100 mV is bad.


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