three weeks ago, Fan speed controls (up / down) on Automatic Climate Control would not work going up to higher speeds. Replaced BLOWER RESISTOR with aftermarket item, and it did not work. Returned DENSO piece to place. Experimented with DEFROSTER: Can achieve HIGH SPEED/maximum fan speed, and work down to lower speeds using down button of fan, but cannot go back up to higher speeds.Fuses are not blown. Fuse blades are clean. Is there an under-hood relay that affects the fan speeds? I don't see anything noted in the icons of the under-hood fuse box cover. Note: The Blower works. The blower works with DEFROST, and will transition to lower speeds using the down button of the fan-speed control. The Resistor had been replaced, resulting in the same low-speed-only/first fan position speed.
Where do I go next?

 

Did you have the same problems when the aftermarket transistor was installed?

 

Yes, same issue after blower motor resistor (how it was named on the parts list) was installed. Is there another transistor/resistor I should be looking for? This resistor is to the LEFT of the Blower Motor, mounted with the heat-sink fins facing toward the firewall.

 

Your car technically has a transistor. The older accords had a resistor and were easier to troubleshoot.

The transistor is controlled by the HVAC panel where you change the fan speed. There is a black wire coming from there that should have a constant ground. You can pull the HVAC control panel to see if the wire or connectors are damaged/corroded.

Take a look at the HVAC circuit board as well. The HVAC circuit board is difficult to diagnose, but I suspect this is your issue.

You may also want to try the self-diagnostic on this thread to help give you direction.

https://www.hondaaccordforum.com/for...94/#post370304