I recently replaced the varriable speed motor on my 2.5 year old Trane 3 ton home ac/heating unit.
It had failed because the idiots who installed it didnt connect the ducting correctly and restircted the return air supply down to about 25%, I am actually surprised the motor last the 2 and half years that it did.

So now the ducting issue has been fixed I can actually hear the air rushing through the vents in the house. So here is my question. Should the blower fan always be on? I can hear it is on even though there is no air flowing, So i am guessing it is just spinning at a slow rate, not enough to blow siginificant air but enough that I can hear it spinning while I am standing under the return air vent.

In the past with the old restricted air flow set up, when the ac unit shut down, I didnt hear anything at all.

Also, an additional question, I was told by the ac guy to use the cheapest air filters and just replace them on a monthly basis as apposed to using the more expensive air filters. Is this good idea?

Thanks in advance...