Blower Motor not coming on. Only 3 volts to speed wire. Relay faulty?

[vacman]

1986 Trane air handler.

The blower motor is not coming on. I am not getting 120 Volts to the speed wire going to my blower motor when fan is called for.

It is a 240 volt motor. It has one 120 volt leg working (black wire) but the red wire leg has only 3 volts. Both legs are supposed to have 120 volts when 'fan' is called for.

I am attaching pics. The relay is the black box in the upper right of the control box. The 2 red wires in positions 3 and 6 are supposed to connect at the contact switch behind them and send 120 volts to the motor on the red speed wire when in fan mode (but only 3 volts getting there, at the end of the speed wire).



It could be the switch is arced, and not sending volts through.

My testing (one probe on ground, other probe at wire connection)  shows 120 volts at the red wire in pos 3 and only 2 volts at the red wire in pos 9 when in fan mode, and the same readings when in 'fan off' mode. That makes sense to me, assuming the contact is not being made in either scenario, so the pos 6 wire remains low voltage. I assume if it were working properly, then in fan mode, I would get 120 Volts at both red wires.


What I want to do is remove the 2 red wires from the relay and connect them to one another (bypass the relay). I would connect them with a 20 amp auto blade fuse, turn on the breaker, and see if the fan comes on.   

Is it safe to use a 20 amp fuse?  Is 20 amps enough?

Thanks



 https://cimg3.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1152x864/air_handler_2_b9662b69b9733c25e8636b62f380c896f633661c.jpg


https://www.hvactechgroup.com/hvacforum/index.php?action=dlattach;attach=2089


https://www.hvactechgroup.com/hvacforum/index.php?action=dlattach;attach=2091

[vacman]

Well, I fixed it. It was the relay. One of the contacts was just 'worn' or something like that. It had a gray look to it. No carbon, no pits. Just a gray circle where the contacts came together.

I used a clean sheet of paper to clean it off. A little bit of gray color came off.

Maybe it was just moving wires around that fixed it, who knows. But the fan works again, and with a minimum of intervention on my part. No wires needed to be removed.

It's intimidating looking into the maze of delicate wires inside the control box. But I got whole box off the wall, and got the relay out of the box, to get a good look at it, get the multimeter probe on it, etc.