There is a great forum on Motor vehicle A/C at www.ackits.com. One of the best forums I've seen on the net. Good MVAC discussion and an interesting off topic board. Good smart people there.
I came across a good home HVAC board a few years ago, but unfortunately I didn't bookmark it and don't remember it.
On the ackits site there is is a guy that posts under the name of MrBillPro. He is a home HVAC tech. Perhaps you could post there and he might be able to answer your question.
Sorry I can't be of more help.