I have a 99 Acura TL ,the problem Isthe heater blower motor doesn’t work. Have tested the motor and it is good we replaced the relay and the 40 amp fuse under the hood! When we bypass everything and run a ground wire it works on low ! Any ideas would be appreciated !

 

There is a section in the service manual that shows how to display any HVAC diagnostic trouble codes in the climate display panel, that would be a good start.

There is also a general troubleshooting page at the beginning of the HVAC chapter that may be helpful; it shows some steps for troubleshooting the blower motor not turning on.

Apologies if this doesn't provide you a direct answer; I always try to go through a complete diagnostic as to avoid buying unnecessary parts.

 

I'm working on the same issue. In my case it was a burnt out connector on the blower motor. I'm waiting on a wiring harness and new blower since the connector on both sides was melted and damaged.

Definitely run the HVAC diagnostic like whitetiger mentioned. Mine comes back with something like blower motor circuit fault. You'll need the manual to interpret the code - and it has some good troubleshooting steps. But in case you just want to look around, common issues are burned out wiring or a bad resistor. I would trace the wiring back and make sure it's all good, maybe pull the resistor out and check it.