I'm replacing my 25 yr old HVAC system and just comleted phase 1 which was the air handler. Heap Pump will be phase 2.

Thus far I've spend 100+ hrs in the learning and planning phase including getting my EPA 608 Universal license.

The air handler I installed was a 4T Rheem RHLA w/20 KW aux. heating. No matter how well you plan there are surprises along the way.

First surprise:

The existing combustable base hole was a little too wide for the downdraft hole in the new air handler. In addition the existing return air plenum was slightly off center. (the old transition piece accounting for this offset). That wasn't too bad - I just make a new combustable base sheet metal panel with a smaller hole and offset it. My new air handler is slightly narrower then the old one. (It would have been easier but I refuse to use tape, mastic or ductboard. I want this to be a top notch installation)

Second Surprise:

The sheet metal plenum transition piece I fabricated wouldn't quite fit. Well after wresting with it I finally got it aligned perfectly. I used Z and S cleats to attach it to the existing plenum. The transition piece has a folded edge and is screwed onto the top of the air handler. (I used a small bead of RP Pro sealant as a gasket for both the combustable base and plenum transition piece.

Third surprise:

The 6 AWG supply wiring didn't have enough slack to connect to the new air handler circuit breakers. We'll after pulling and peeling back some conduit I got just enough slack to get it securely connected. Trying to get a few inches slack from 2 - 2condustor 6AWG cables inside a wall is pretty hard pulling.

Fourth surpise:

I completed the installation and fired it up by jumpering fan (G) to red. Motor comes on and it performs as expected. Then I turn off the circuit breakers at the wall panel to complete some wiring clean up. I turn the breaker back on and one pops off. OK, I turn the second one off and inspect everything and all is OK. Same thing happens again. I turn off the panel breaker and then turn off the air handler's own breakers and switch the panel breaker on and it pops off. I ohm out the line thinking there's a short from L1 to L2 or Gnd. However there isn't one. So I decide to switch breakers in the wall panel to see if it's the breaker or the circuit. The same breaker now pops on the second circuit. OK, I figure these breakers are as old as the old air handler so go to Home Depot and buy 2 new 60 amp panel breakers. That solves the problem.

Fifth Surprise:

New breakers stay on but now the air handler won't come on in fan mode using my jumper. I don't see anything abnormal and it worked before so I test for 24VAC from the secondary xformer and it's good. I try the energize the fan again but it doesn't come on. Now I'm thinking I blew something on the control board so I inspect it and check all the components I could. (diodes, resistors, etc). It still doesn't work so know I think I've toasted the GE X13 motor or control ciruitry. I look again and this time I see a wire connector has slipped off the motor connector. The Rheem schematic doesn't match the labeling on the GE motor but I figure it out. Now everything works fine and this time I secure the motor's wire bundle to the frame using several tie wraps.

Sixth Surprise:

Now I turn the power off to install the cover over the control board. I tun power back on and it's buzing like crazy. OK, I think I shorted something out but don't see anything. We'll it turns of the metal cover is amplifying vibration from the 24VAC xformer. OK, I reinforce the cover to dampen out the vibration and that works.

No more suprises and I performs great. I'm very pleased with the installation. Heat Pump comes next.

This Air handler installation took about 16 hours including fabrication of the transition piece. It sure gives me respect for the guys that do this for a living. It's hard work and there are plenty of challenges along the way.