The HVAC guy may have put whatever he had on the truck that was closest to the one that needed to be replaced.
Unfortunately, there may be no telling what the correct rated cap is suppose to be.
This is a common problem where parts start drifting from the correct specs.
For example, the old cap may have been 8.5 MFD and 7.5 MFD was all he had at the time. Now some one else may show up and not have a 7.5 MFD and install a 6.5 MFD thinking that it's only 1 MFD difference when in reality, it's 2 MFD difference.
If you get lucky, you may be able to read the nameplate off the fan motor and see if it specifies a cap rating or contact a contractor that deals in Trane and see if they can tell you what the proper specs are.
Last edited by kok328; 05-20-2012 at 05:08 PM.