Hello my friends,

I'll get right down to it. Owned home a year now, and I don't believe blower control circuit is set up right. Replaced plenum switch in winter, because the blower was not kicking into high when plenum was hot to disperse the heat. Now in summer with a/c... same problem. The blower do not kick into high when a/c turns on... this in turn causes my condensate line on my condenser to freeze outside... thus inhibiting cooling. I can place the fan into high manually of course through the plenum fan switch which will prevent this from happening. My blower also runs in low 24/7 which I'm not happy about. Can anyone help me with this. This is how I would think it should work, and please correct me if I am wrong. Blower does not need to run all the time, especially when no heat or cooling is being called. When heating, blower should run at low speed until plenum switch heats to a specified temperature range (which after replacing the switch I am certain is set correctly) at which time the blower kicks into high speed. In summer time, the blower should kick into high speed whenever the a/c turns on.
I have attached some pics of the control set up which I hope will help you... help me. Thanks

Attached Images

   

Actually most furnaces are set to run on low blower speed only in the heat season since hot air normally rises. In the cooling season most properly setup A/C syatems run on medium speed but depending upon duct work etc some systems will need the high speed for cooling.

From the looks of the pictures you have what I call a rats nest of wires with a add on relay probably for the A/C blower motor to come on. The only thing you can do is test the components to find out which is defective causing the problem. Since I am not there I cannot do the testing for you.