Electrical
11
Switch
In order to bench test a switch, the way it operates must be known. All switches either open a circuit or close a
circuit. The difference between switches is their resting state and how many circuits they control. When the switch
controls more than one circuit, it could have one side normally open and the other normally closed. It could also have
all sides the same.
A switch that while resting (off) closes (has continuity or allows current to flow through it) a circuit is called a nor-
mally closed switch. When the switch is activated it will open the circuit.
A switch that is open (does not have continuity) when in
a resting state is called a normally open switch. When acti-
vated, the switch will close the circuit. The tabs for a nor-
mally open switch generally are unmarked.
The switch used on the snow flurry snow throwers has
three terminals. One is a common terminal, one is a NO
terminal and the last one is a NC terminal. See Figure 2.9.
Testing the switch
When testing the switch, treat it as two switches; the common terminal and the NO terminal as one switch and
common to the NC terminal as another.
To test the switch:
1.
Disconnect the power supply.
2.
Remove and open the switch box assembly by following the steps described in the switch box section of this
chapter.
3.
Remove the switch from the circuit.
4.
Set the DMM to the ohms scale (
Ω)
.
5.
With the switch in the off position; touch one probe to one of the common tabs and the other probe to the NC
tab for that circuit.
NOTE:
The DMM should read zero resistance.
6.
Move the probe from the NC tab to the NO tab.
NOTE:
The meter should show an open circuit.
7.
With the probes still attached, turn the switch on. The readings should reverse, NO should have zero resis-
tance and a NC switch should indicate an open circuit.
8.
If the switch fails in any of the tests, replace the switch.
NOTE:
The part number for just the switch is 725-05222.
9.
Install the switch box assembly by following the above steps in reverse order.
10.
Test run the snow thrower before returning to service.
Figure 2.9
COM
NO
NC
For Parts Call 606-678-9623 or 606-561-4983
www.mymowerparts.com
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