Checking a window unit fan switch

I use an aligator clip to L1-top leg of switch below (makes it easier to hold the switch while checking the legs on the other end).

I set my meter for ohms and mine has an audible tone when I get continuity. That is a good thang.

I connect one lead of the meter with aligator clip to the L1 leg (usually off by itself on the end of the switch). In the off position I should not get a reading on any of the legs opposite of L1. I turn the switch to fan only and I get a reading between L1 and 1 of the 4 legs on the other end(usually black or high). The middle bar by the way is a dummy post, and only holds the fan and compressor common wires, and L2 (power), no need to check it because it is not connected to anything inside the switch. It is mounted in the middle for convenience and usually has 4 male clips for spade connectors on it. I go to the next position on the switch and I should get a reading on 2 of the posts. One for compressor and another for 1 of the various fan speeds. Most of the time the compressor leg will be toast IF you suspect the switch to be faulty. It is good to know how to check these and how they work.

 typical rotary selector switch

Oh! If you forgot how the wires went, remember this: L1 will have one leg of the power cord and the dummy post will carry the other leg of the power. Black is always high fan, blue is medium fan, red is low fan, and yellow is compressor leg to thermostat, easily ID'd by the short wire going to the thermostat. A white common from fan goes to the dummy post and a white common from compressor goes to the dummy post,and L2 goes there so the power will feed both the compressor and fan back to source. So you have 3 wires on the dummy post total, this feeds both the compressor and fan. The other hot leg goes on L1 and the rest of the wires (usually smaller in diameter for the fan's various speeds) control the speed and compressor.

 On these newer models with a small computer board, the connections are basically the same. These clever folks hide the fuse by the way, under the backside of the board so look hard for it. If you do not wish to spend the money on a board, you could hotwire the thing. Tie your 2 commons together with one hot leg and tie black fan(for high speed) and the compressor wire into the other side of the power cord and be cool. To kill all power to the unit when the house is cool just connect a cheap line voltage type thermostat to the unit.  Simple ain't it? LOL

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