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TMADP-0240-3WS - Installation Instructions

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3-Way Switch + 24 Hour Timer–Damper Control 

Easy to Follow Installation Instructions for the

HMI HOYME Adaptor TMADP-0240-3WS  

A Forced Air Heating System having a Fresh Air Intake Duct leading into the return plenum is often equipped with a Power Open Damper. Usually the thermostat causes the damper to open for fresh air during furnace firing and allows the Damper to close when the fire stops. To open the Fresh Air Damper at times when the furnace is not firing requires the use of a 3-way switch (SPDT). This Timer/Adaptor, however, has been designed to override the normal operation of a fresh air damper to remain closed at certain intervals of the day due to the reoccurrence of foul outside air.

Purchasing a 3-way switch and the necessary extras can be time consuming. By purchasing this Ready Mounted 3-way switch with an interval timer, TMADP-0240-3WS, you have eliminated the trouble of buying a 3-way switch, an interval timer, an electrical enclosure, all separately plus making the necessary connections and the problems of assembly. This adaptor comes completely assembled with simple, easy-to-follow installation instructions which follow:

1. Mount the Adaptor TMADP-0240-3WS in a convenient place to operate the timer on or around the furnace area with two screws supplied.

2. Inside the adaptor are terminals “W”, “C” and “R” which are to be connected to corresponding terminals inside your furnace. Use 3-C 18Ga. thermostat wire.

3. Connect adaptor terminals “#2” and #4 to the two wires on the motor of the Hoyme Damper (Power Open Only).

*Automatic Setting: When the Adaptor switch is in the“Automatic” position, the thermostat will operate normally which will cause the damper to open during the heating cycle and will allow the damper to close when the fire stops.

*Manual Setting: In the “Manual” position, the switch will override the thermostat and will power the damper to remain in the open position.

*NOTE: Engaging the Timer by positioning the white pins outward overrides both the “Automatic/Manual” settings of the 3-way switch and the thermostat to keep the fresh air damper closed during times of foul outside air.
See “Interval Timer” page 2.

This Schematic Wiring Diagram in also on the Inside Cover of the Adaptor

Interval Timer

In addition to the white pins which may be pulled outwards to override both the 3-way switch and thermostat, there is another pin (switch) located in the centre of the timer face as shown by the Red Arrow.


There are three positions for the centre pin. The normal position is in the ‘middle’. In this position the timer will operate as it should. Each white pin extended outwards on the periphery will keep the damper closed 15 minutes.

The centre pin placed in the up ‘ I ’ position will cause the timer to act as if all the white pins were extended. This will override both the 3-way switch and the thermostat. The damper will remain continually closed.


The centre pin in the down ‘ 0 ’ position will override the white pins causing the timer to have no effect on the circuit. Therefore both the 3-way switch and the thermostat will have full control of the damper to open and to close.

(For Adaptor applications, see Color Wire Diagrams #3A3; #4A3 & #8C4.)


Installation instructions - Printer friendly (pdf)

TMADP-0240-3WS - Information Page

Last Updated (Friday, 01 April 2016 09:42)