I've read the posts with the opposite issue, which have been helpful (you guys are amazing!) but still no solution. Problem is that the blower fan does not come on when system is on "Cool" and fan is on 'auto' or when system is on "Off" and fan is on "on". Interestingly, we discovered fan comes on when system is on "Heat" and fan is on "auto".
Things I've checked and tried:
- Replaced thermostat first; no issues w/ install
- Blower motor capacitor was weak but have now replaced
- Tested motor by testing common wire to each of the speed wires (High, Med, Low), all showed about 7-10 ohms
- Relay seems to check out, and the switch does go on/off when we turn the fan "on" or "auto" on the thermostat. So I think the thermostat is working fine, but fan still doesn't come on.
- Since the issue seems to be on the cooling/fan side, I was convinced that we had an issue with one of the green or yellow wires connecting the thermostat to the relay or the relay to the fan/main limit, etc. So I tested continuity on the connecting wires by disconnecting for example, the orange between whatever you call the terminals where the thermostat connects and the bottom of the relay. I tested continuity on 5 different yellow or orange connectors, and all looked fine (i.e. 0 ohms).
- Longshot, and earlier in the process, I tested the Door Interrupt Switch and it was fine.
I must not be understanding some part of the wiring that affects cooling and the fan, but not the heat. Could the Fan and Limit Controller be the culprit? I am guessing not, because it seems that this relates to heating (a shutoff if plenum gets too hot, right?) but would not affect cooling or just running the fan. I am so frustrated... could use your help. thank you so much.