Please help me change my furnace blower speed

[ajm786]

I have a Ducane MPGA125B5B furnace. I had it installed about 2 years ago. It is a great furnace and has served its purpose well over the past 2 years, but there is slight annoyance we have with it: It's TOO LOUD.

I want to change the speed of the blower to medium from its current setting of high. I have the manual, and I looked inside, but there is not really any place that describes how to change the blower speed.

If I'm correct, in the furnace wiring specs, it shows 3 diagrams and says directly above it "FACTORY SETTING HEAT SPEED". I'm not sure if this is what I need to be changing, so I tried it anyway. I followed the wiring specs for the Medium Speed Heat, but it made no difference. The funny thing, is that the way its wired up now doesn't even follow the specification's settings for the High Speed Heat; it's wired differently.

Right now, here's how it's hooked up:

Blue > Heat
Black > Cool
RED wire set to middle Park jumper

At this setting, the speed of the furnace is High.

Even though I tried moving the RED wire to the Park jumper far to the right (there's only 3 settings), it didn't make a difference.

Any help would be appreciated.

[Senior Tech]

No diy. Call a pro before you damage something.