G15 This power point presentation is designed to assist the student in understanding the relationship of the fan and limit switch to the fan relay, when used in conjunction with heating and cooling equipment.

The next slide will show page G15. There are five (5) independent circuits on page G15. This presentation will consider each of the five and what the unique features are to each one of them. Please advance to the next slide.

The next slide will begin the process of taking a look at the five(5) circuits and their unique features. Please advance to the next slide to observe the first circuit.

You should observe the following characteristics on this schematic. 1.The motor is single speed and since it is low speed, this would be a heating only application. 2.The fan switch and limit switch are both connected to the line.

Since the fan switch and limit switch are both connected to the line, there would be a jumper from the fan switch to the limit switch. There would be NO need to bring L1 to both controls.

Observe that L1 comes to the ‘LINE’ side of the fan switch (FS). and that L1 is ‘jumpered’ over to the ‘LINE’ side of the limit switch (LS). You should also observe that the fan switch (FS) is ALWAYS normally open (NO) and the limit switch (LS) is ALWAYS normally closed (NC).

The next slide will begin the process of taking a look at the second circuit. Please advance to the next slide.

You should observe the following characteristics on this schematic. 1.The motor is single speed and since it is low speed, this would be a heating only application. 2.The fan switch and limit switch are NOT both connected to the line.

THEREFORE, there is NO jumper between the FS and LS. 1.The FS (FL normally open contacts) has its ‘LINE’ side connected to L1. 2.The LS (FL normally closed contacts) has its ‘LINE’ side connected to ‘W’ of the thermostat.

Let’s review: 1.The first circuit has the FS and LS in the power circuit with heating only. Therefore, a jumper is required. 2.The second circuit has the FS in the power circuit and the LS in the control circuit. Therefore, NO jumper is required, because you do not want to mix 120v and 24v.

The next slide will begin the process of taking a look at the third circuit. Please advance to the next slide.

You should observe the following characteristics on this schematic. 1.The motor is two speed and since it is two speed, this fan would be able to provide heating and cooling. 2.The fan switch and limit switch are NOT both connected to the line (L1).

You should observe the following characteristics on this schematic. 3.The fan switch (FS) has line voltage coming to its ‘LINE” side from the NC fan relay (FR) contacts. 4.The limit switch (LS) has low voltage coming to its ‘LINE’ side from the ‘W’ terminal of the thermostat. 5.The fan relay (FR) has a SPDT switching action.

You should observe the following characteristics on this schematic. 6.The fan relay (FR) has power coming to its ‘LINE’ side from L1. 7.When using a SPDT fan relay (FR), the fan and limit cannot have a jumper, because the fan switch (FS) has power coming to it from the NC contacts of the FR. More on this later.

The next slide will begin the process of taking a look at the fourth circuit. Please advance to the next slide.

You should observe the following characteristics on this schematic. 1.The motor is two speed and since it is two speed, this fan would be able to provide heating and cooling. 2.The fan switch and limit switch are both connected to the line (L1). Therefore a jumper could/would be used. Left click to observe the jumper.

You should observe the following characteristics on this schematic. 3.The fan relay (FR) switching action is a DPST – 1NO, 1NC. 4.Note that when the FR switching action is DPST, the NO contacts go directly to ‘Hi” speed. 5.Note that when the FR switching action is DPST, the NC contacts go to the ‘Lo’ speed, BUT power comes to the ‘LINE’ side from the fan switch (FS).

Note the fan relay (FR) NC contacts go to the low speed. Note the power comes to the “LINE’ side of the FR from the fan switch (FS). Note the fan relay (FR) NO contacts go directly to ‘Hi’ speed.

The next slide will begin the process of taking a look at the fifth circuit. Please advance to the next slide.

You should observe the following characteristics on this schematic. 1.The fan relay (FR) switching action is SPDT. 2.The fan switch (NO contacts labeled FL) are after the FR normally closed (NC) contacts. 3.The limit switch (NC contacts labeled FL) are in the power circuit. 4.There is NO jumper on the FS and LS because the ‘LINE’ side of the LS is coming from L1, and the ‘LINE’ side of the FS is coming from the NC contacts of the FR.

In conclusion: 1.A jumper on the FS and LS is determined by the circuit the LS is found in. The FS will ALWAYS be in the POWER circuit, but the LS can be in either the POWER circuit or the CONTROL circuit.

In conclusion: 2.A jumper on the FS and LS is also determined by the switching action of the fan relay (DPST or SPDT).

In conclusion: 3.The switching action of the fan relay (DPST or SPDT) becomes a contributing factor in the way the fan circuit is wired.