Originally posted by nyrfan
OK so let me be sure we are on the same page:
Return = Where the air gets sucked into the unit (78)
Air Handler: Unit inside my garage (Where I change the air filter (55.9). BTW: I tested this by sticking a thermostat into the unit where the serviceman put his in.
Register: Ceiling duct providing the air: 62.5
Now if that's correct can I just assume it's the high heat and lack of attic insulation and?
The return register is the grille where the air gets sucked into the return duct work, which is routed through your attic and connects to the return plenum (the metal or duct board box connected to your air handler / furnace) in the garage. The supply plenum is connected to the air handler / furnace and thence to the supply duct work, and the supply registers.
You have a 6.6 degree drop in your supply duct work. If you measure at the return plenum we can see how much heat gain we have in the return duct work. The heat gain can be caused by poor insulation or even leaks in the ducting.