Near the end of September is when most people shut down their central air conditioners for the year. Michigan in October isn't likely to be warm enough to need it. This is not a big job, and requires no particular handyman skills.
The first thing is to electrically disconnect the condenser (outdoor portion of the system). All A/C systems should have an electrical disconnect box near the condenser unit, usually within arm's reach. Most of them open by sliding back a latch, then sliding the front door of the box down, and swinging it open. Be careful!. If the inner cover is missing, you could find exposed, energized electrical equipment in that box. The box will either have a switch-like circuit breaker or a pull-out fuse block. If it's a breaker, just turn it off. If it's a block, pull it out by the handle and put it back in upside down. This process protects the unit from accidental start-up in cold weather, which could damage the most expensive part, the compressor. Also, some units have small heating elements in them to keep the compressor oil warm between use cycles. There's no point in running this all winter. Next, put a reminder on your calendar to turn the unit back on by the 15th of May or so. The units with compressor oil heaters won't be willing to start until several hours after the power is restored, so don't wait until you need the A/C to reconnect the disconnect. The last item is to cover the outdoor condensing unit to protect it from tree debris, etc. during the off season. The cover needn't be air tight or even run all the way to the ground, as long as it covers the top.
The next chore is changing or cleaning the furnace filter. This is a good time to find the furnace's service switch. It looks like a regular light switch, and usually lives on the side of the furnace. Sometimes it will be on the ceiling or a nearby wall. Turn it off before you stick your hand into anything mechanical-looking.
If the installer of the furnace was a nice guy, he created a slot in the return duct next to the unit, to allow you to change the filter without opening the furnace cabinet. You will see the edge of the filter, and you can just slide it out and slide another one in. No slot? OK, you have to remove the lower part of the cabinet front. Usually these slide up first, but manufacturers try to make this as difficult as possible. Be persistent and patient; violence really doesn't help!
If the furnace was built after 1980, you will notice a little switch behind the edge of the cabinet door as you remove it. This is a simple kill switch, and its job is to keep the furnace from running if the door is off. This was a good idea, because running the furnace with the door off can pull fumes and flames right out into your living space! However, if you don't get the door back on just the right way to compress that switch, your furnace will refuse to run!
The filter will usually have little arrows printed on its outer edge that indicate how the filter is installed in the "air flow". If you put the filter in backwards, it is more likely to get torn apart by air drag as it clogs up. But how do you know which way the air flows? Well, Dr. McCoy, it's simple logic! The purpose of the filter is to protect the furnace from dust. It is therefore installed just upstream of the furnace. In other words, the arrow on the filter should be pointing toward the furnace, not away from it.
Do you have a digital thermostat? If you do, go up and look at it now, while the service switch is off. Many of them will show a 'batt' flashing on the screen, to indicate that the stat's normal power source (the furnace control circuit) is off, and that it's running on its back-up battery. This is proper. If the thermostat's LCD display is blank, it means its battery is dead or missing. (If the 'batt' flashes when the furnace is running, it means your furnace controls have a wiring problem.)
Some people want to turn on the water supply to the humidifier now. Bad idea! Next month's letter will talk extensivly about humidifiers, but for now suffice it to say that its best left off until you can feel noticeable dryness in the house. That won't happen in most houses until after Halloween. Maybe after Thanksgiving!
Ok, the new filter is in place. Put the door back on, and turn the service switch back on. Check around the furnace and its vent connector pipe (the one running to the chimney) to make sure nothing flammable is nearby. Test the basement smoke detector. Ready? Test the furnace by cranking up the thermostat to 5 degrees above present room temp. If the unit doesn't respond in a few minutes, double-check the blower door switch. No luck? Ok, it's time to call for service.
Actually, now would be a good time to call for your annual professional maintenance visit. Don't wait for frost. Right now, there are thousands of furnaces out there with failed components in them that barely limped through last season, but won't start this season. On that first frosty morn, each one will be an urgent service call. The law of supply and demand will jump up and bite you in the wallet if you wait.
Enough for this month? OK. Incidentally, back issues of this will soon appear on ye olde website, at www.inspectmichigan.com. Check it out if you haven't been on the list since June.
Matt