I have a variable speed fan on my Lennox 5 ton unit and it runs too slow to cool the house correctly with all the ductwork I have. The house is a tri-level and about 2600 sq. ft., with only this one unit. I need to up the speed on this fan to keep me cool. Can I do this?

If you have a true factory variable speed fan setup it should only be adjusted by using the proper tools which I am sure you do not have. The original installer should have set the speeds up for you during the install process. I would also like to ad that a higher speed will not guarantee better cooling since moisture removal is of prime consideration for actual comfort.

Now if you have the simple 2 or 4 speed motor you could just change the speed selection wires but that is not the way to change the speed on a true variable speed unit. I would also like to mention that damage can be done on some variable speed setups especially if you try to increase the speed range when the duct static pressure in high. The price of a variable speed motor and controller can be up to 1000.00 and that is a big risk to take.

Hvac1000 told the truth. the variable speed motor can take it and the board out if wired or set wrong. The $1000 dollars is a low estimate if you take them both out. I have seen many home owner cry after taking them out only to find that the system was under warranty until the tried to do it their self.

Always pray for one of those jobs when the truck payment is due.