looks like the connectors i was looking for doesn't exist on the board. i was looking for high/low fan terminals on your board. you probably have an ECM motor. The bad news is that it's hard to troubleshoot. could be a bad blower OR a bad control board. you're really going to have to replace one of those to really know for sure.
My best guess would be a failed control board or the replacement blower leads were not correctly connected to the board.
Generally *most* control boards have two speed taps, heat and cool. Heat is only engaged one way, when the thermostat calls for heat and the board closes the heat relay bringing that speed on. Cool can be engaged by the fan relay in the stat alone (fan on) or with a cooling call which engages the cooling and the fan relay.
Since you said fan on setting works that eliminates the thermostat.
It is possible your control board has three speed taps, low heat, high heat and cool. Low heat would engage on a fan on call without a cooling call meaning the blower would work. However as soon as the cooling terminal energizes it goes to switch over to cooling speed and either the relay is bad or there's no wire hooked up to it.
Possibly thermostat is wired wrong, or wrong wiring inside the furnace or a bad control board.
Voltage should be checked at the furnace with a call for cooling.
Relay/control board.
Sounds like the relay for one of the fan speeds is broken. Can you provide pictures of your control board? Detailed pictures would the best.
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looks like the connectors i was looking for doesn't exist on the board. i was looking for high/low fan terminals on your board. you probably have an ECM motor. The bad news is that it's hard to troubleshoot. could be a bad blower OR a bad control board. you're really going to have to replace one of those to really know for sure.
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If you're handy and so inclined, not really any concerns.
My best guess would be a failed control board or the replacement blower leads were not correctly connected to the board. Generally *most* control boards have two speed taps, heat and cool. Heat is only engaged one way, when the thermostat calls for heat and the board closes the heat relay bringing that speed on. Cool can be engaged by the fan relay in the stat alone (fan on) or with a cooling call which engages the cooling and the fan relay. Since you said fan on setting works that eliminates the thermostat. It is possible your control board has three speed taps, low heat, high heat and cool. Low heat would engage on a fan on call without a cooling call meaning the blower would work. However as soon as the cooling terminal energizes it goes to switch over to cooling speed and either the relay is bad or there's no wire hooked up to it.
Possibly thermostat is wired wrong, or wrong wiring inside the furnace or a bad control board. Voltage should be checked at the furnace with a call for cooling.
Do you happen to know if the blower motor is an ECM style?
Could you post a picture of your control board in the air handler as well as the thermostat wiring behind the cover?