I recently purchased a condominum unit with a very old air conditioning system (1980's).
A home inspection revealed a return/supply difference of only 13 degrees. We requested that a licensed HVAC contractor come to inspect the unit (in particular the return/supply temp difference) and were given a brief "it is fine" type receipt. Not very convincing to say the least.
We had our own contractor come out this afternoon, and the return/supply difference was only 11.9. He said there is obviously a problem with the unit. The real estate contract required a functional unit.
The HVAC contractor said the return and supply difference should be anywhere from 18 to 20 degrees, and we are way under that. I have also read as low as 15 degrees. I was wondering what the pros consider an acceptable difference? Also, do you have any links to this in writing since we may need to cite a difference?