Late Thursday night, we noticed a burning smell in the house. No, there wasn't a fire in the house. It smelled like something other than food had burned and left its odor behind as evidence. We searched for its origin and discovered that the odor was strongest in the warm air blowing from a floor vent. This particular vent also happened to be closest vent to the outdoor HVAC unit. So, naturally, I assumed that a mouse had crawled into the unit in search of heat, fallen on the heat coils, and toasted.
NOTE -- I am not out of my mind and that's not a completely obscure conclusion to arrive at. Last winter, I opened the unit for service and discovered just that. A cooked mouse was wedged under the heat coils, which explained the burning smell in the house just prior to finding that. However, the stench from that incident had a subtle undertone of death. I suppose it was wishful thinking to assume roasted critter rather than broken heater.
Anyone who enjoys home repair as much as I do will empathize with knowing that I had to wait until Saturday to investigate, diagnose, and repair. My days were filled with work until the sun was down. The nights were entirely too cold to work outside. Late Friday night, my fiancée and I both notice that the new burning smell had gone, our slipper encase feet were frigid, and no air was circulating. The reality of the situation quickly set in. It's almost midnight, the outside temperature is in the 20s, and our heat hasn't been working for the last several hours...damn.
If you don't have or can't find the owners manual for you HVAC unit and don't know what it is, don't panic! The brand and general model type will likely be on the outside of the thermostat. Take the face off the unit and look for a more specific model number. Mine was printed on the circuit board. Using your favorite search engine (I prefer Google), search for that model number. You will likely find the owners manual and installation instructions. Both will provide ample information to begin the diagnosis process. HVAC for Beginners was very helpful. There was nothing I could do that night. We holed up in the bedroom, layered up the blankets, and prayed for the insulation to do its job.
I could not of asked for a better Saturday morning to work outside. The sun was out, the breeze was light, and the temperature was tolerable. Thank you, God! As far as I know, there is only one store in town (A-1 Appliance) that carries parts for my unit, keeps them in stock, and is open on Saturday. After speaking with the briefly, it was determined the the motor that drives the scroll fan had burned out (thus explaining the smell and lack of air circulation in the house).
Let's get to work.
Tools Required - screwdriver, ratchet set or wrenches, wire strippers, fan blade puller, lots of patience
1. Cut power to the HVAC unit at the breaker. It is most likely mounted to the side of the house, very near the unit.
2. Remove top and side panels.
3. Remove heating coil rack.
4. Remove scroll fan assembly. It should slide right out.
5. Take careful note of the wires going to the motor and mark them with tape if necessary. Mine were all colored. You may notice that there is a large capacitor attached to the scroll fan assembly. Remove that, as well, and disconnect the wires. If the capacitor had blown and the motor was still good, it will be obvious upon visual inspection.
6. With exception to the capacitor wires, cut the wires going to the motor, leaving a couple inches just in case you need to reattach it.
*** The next few steps can be completed in the comfort of your garage or other work area. ***
7. Rest the scroll fan assembly on its top and you will notice a metal band holding the motor in place. This band is held tight by a single nut and bolt. It is an incredible pain to get too. I cut my knuckle open in the process. You have to get this loose because the model number for the fan is underneath the band.
8. Go buy the new motor. It may require a new capacitor. Your supplier should also provide you with a wiring diagram. The new motor might also have wires that come out from the base of the motor, connect to themselves, and go back into the base. These control the spin direction. Swapping these wires changes direction. Leave them as they are for now unless you know they need to be swapped.
9. You must now free the motor from the scroll fan. This is very tricky if you don't have the proper tool, as the motor fan has a very tight grip on the shaft. DO NOT USE A HAMMER!! The metal composing the motor shaft is very soft and will mushroom over, thus making it impossible to remove without further employment of a hand held grinding wheel or Dremel. What you need is a 5/8" Steel Center Fan Blade Puller. I am extremely fortunate to have a neighbor with a fully stocked workshop who also used to repair HVAC units.
10. Insert the new motor and tighten the band clamp to a point that you can still slide the motor around. Why? You'll be adjusting it to its correct position.
11. Center the fan is centered axially so that it won't doesn't touch the sides of the assembly while spinning. If it's not centered, it will behave like a washing machine with a pair wet jeans wadded up on one side. You know what I'm talking about here. This will cause the scroll fan to scrape against the side, scream like a banshee, and eventually vibrate itself into pieces.
12. Center the fan vertically so that air will only flow in from the top. If air leaks in from the bottom, you'll get an unpleasant mixing effect that will cause your unit to work harder than it has to and rack up the power (if not breaking it in the process). Once again, ensure that the scroll fan is not touching the assembly for the same reasons mentioned above. Scrolls fans are not cheap to replace and just as much of a hassle! You'll know you've done a good job if you spin the fan and it moves quietly (no metal scraping).
13. Reassemble the scroll fan assembly (if you took yours apart). Feed the wires through the bottom and zip tie them in a similar fashion and location that they were originally found in. Thicker zip ties hold up longer when exposed to the elements.
14. Attach the new capacitor. It should fit where the old one was. Plug the wires into the capacitor. They are the only 2 wires coming from the motor that have plugs on them and it doesn't matter which terminal they attach too, so long as it's not the same post. Strip the rest of the wires back about an inch. Attach the ground wire (the green one) to the scroll fan assembly.
*** Let's go back outside ***
15. Slide the scroll fan assembly back into place and secure with the screws you removed earlier.
16. Connect all the wires as illustrated by the wiring diagram and secure with wire nuts. You might also want to secure the wire bundles.
17. Reattach the heat coil.
18. Turn the unit on to test your work. Shoddy work might become obvious at this point. If there is a strong air stream blowing up from the scroll fan, you have a problem. This mean that the motor is turning in the wrong direction and will be vacuuming warm air from the house rather than blowing it in. This is easily fixed. Remove the fan assembly and switch the direction wires.
19. If everything works fine, reassemble the remainder of the unit by putting the panels back on.
20. Pat yourself on the back. You have successfully repaired your HVAC unit and saved $300-$500 by not calling a repairman.
This entire project shouldn't take more than an afternoon. I unfortunately had to wait for my neighbor to come home that evening to get to his fan blade puller. Just for effect here, imagine what it's like to reassemble everything when it's below freezing outside, dark, and the unit is blowing on your hands.
The next day it started snowing and didn't stop...for 2 days!
Well, I'm impressed.
ReplyDeleteFriday night was SUCH a cold night! I'm glad that someone was able to fix the HVAC that Saturday :)
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