You state the original motor overheated when the insulation fell on the housing. Are you sure about this? I would think the motor would no longer operate if the internal mechanism became so hot to give off a strong smell. Are you sure the new motor is overheating? Does it feel very hot when you touch the housing? You stated you have changed the motor from a 1/3 HP to 1/2 HP. Have you set the air flow so that it is the same as the 1/3 HP motor? The smell may be coming from something unrelated to the motor. If the smell is giving you a headache then you should have a professional inspect the heat exchanger. You may have a more seious problem.

I would suggest getting a new blower motor on order now. It sounds like yours is going out. I can give you a contractors price on one if you know what size you need or I can cross reference if you give us a call 866-777-0074 The effect of adding to much oil is the same effect that if you add to much oil to a car. It will become sluggish, ineffecient and gummy. I am still loading all of your blower motors online so if you don't see what you need please call. Good luck aw Here is a link that might be useful: Blower Motors

Thanks for all the opinions! There are several "drop-in" ECM motor replacements, the electronics (i.e., control board) are self-contained in the motor. So the electrical interface is the same as the mutli-wire one for induction motors. My concern is that the drawing for the Emerson doesn't show mounting holes drilled where my PSC motor has them, and I'm not interested in voiding a warranty by drilling into a new $350 motor (they're not cheap). The furnace is 10 years old and is working well, especially after I solved the condensate leak problem by using quality hoses and stainless hose clamps (and high-temp RTV silicone), unlike the way the factory did it.

The "delta T" is referred to as the split temperature - the difference in temp between the air before the a/c coil and after the a/c coil. Your split temps are good. The slower air speed will provide better dehumidification and cooler temps coming from the a/c coil. You can get the manual for the air handler from Lennox (or look at the wiring diagram inside the air handler) to find out what speed your fan is set on (low, med, med-high, high). I believe that the "24" in "10ACB24-9P" means that it is a 2-ton unit (24,000 btu). I think that a rule of thumb is 300 cfm (cubic feet per minute) of air volume per ton so 728 cfm for 2 tons looks OK. You can ask the builder to check CFM with the new fan setting. You can also ask him to calculate your "superheat" which tells you how the evaporator coil is performing with regards to refrigerant charge. My 3 speed Goodman air handler is set to low. I have all-metal ducts and a 2 story home so low speed works for me. I had to re-read your post to see that it was the return grills that are vibrating and not the supply vents. Has the vibration stopped with the lower fan speed? Best of luck to you.