Please retrieve a copy of page A8 from the Student Handout Packet.

Page A8 has various combinations of fan/limit circuits in the way they can be wired. It also has various fan relay circuits in the way it can be wired. So this presentation will review these wiring arrangements.

Begin with the circuit in the upper left corner.

This is a simple heating only application. Notice the fan switch is identified as FS and the limit switch is identified as LS. The jumper would be installed on this FS/LS, whether from the factory or done in the field, for the convenience of less wiring. The FS and LS are both in the POWER circuit.

Moving onto the circuit in the upper right corner.

This is also a simple heating only application This is also a simple heating only application. Notice the fan switch is identified as FL and the limit switch is identified as FL. The fan switch would be the OPEN contacts and the limit switch would be the CLOSED contacts.

In this wiring arrangement, the JUMPER would be REMOVED because the fan switch is wired in the POWER (120v) circuit and the limit switch is wired in the CONTROL (24v) circuit.

Moving onto the circuit on the middle on the left.

This circuit is for heating and cooling This circuit is for heating and cooling. So this involves the fan switch, limit switch and the fan relay. This circuit has a lot going on with it. So continue through the slides to discover all the details.

Starting with the Fan Relay (FR). What is the switching action?

You should have answered SPDT You should have answered SPDT. There is one input and two outputs, one output CLOSED and the other one OPEN.

Now move onto the FL. Is the jumper in or out?

You should have answered out for two reasons You should have answered out for two reasons. Reason one: the fan switch is in the POWER circuit, and the limit switch is in the CONTROL circuit.

Reason two: the output of the fan relay NC contacts go onto the fan switch.

Notice also that this circuit would be the same for either 120v or 240v. Obviously, the fan motor would be rated for the application.

Moving onto the circuit on the middle on the right.

This circuit is for heating and cooling This circuit is for heating and cooling. There are two MAJOR differences in this circuit from the previous one.

Does the fan switch (FL) and the limit switch (FL) have the jumper? The answer is: YES

What is the switching action of the fan relay (FR)?

The line side of the NO contacts are connected to L1. The line side of the NC contacts are connected to the NO contacts of the FL.

Answer: DPST

Moving onto the last circuit on the bottom left.

This circuit should look familiar because it is similar to the one right above it on this page A8. Can you find the difference?

The difference is that in this circuit, the limit is in the POWER circuit, but in the circuit above it, the limit is in the CONTROL circuit.

In conclusion, the objective was for you to become more familiar with fan switch, limit switch and fan relay wiring configurations. Did you?

The End