How to Wire AH3 OFF-Delay Timer and Relay with Boiler Fan?

Wiring AH3-3 Timer for OFF-Delay Operation with Boiler and Fan

The main purpose of the circuit is to automatically turn off the wall fan when the boiler switches off, using of an AH3 timer that provides an ON-Delay mechanism. This identical design can also be used to supply air to the heat pump in the water heater.

The OFF-delay refers to delaying the switching-off operation for a specified time. For example, the load does not shut down immediately but instead waits until the preset time duration on the timer has expired.

In this wiring configuration, the setup requires an additional general-purpose (8-pin) relay with both normally closed (NC) and normally open (NO) contacts. Ensure that you choose a relay with the appropriate rating and size, considering a coil voltage that can be safely controlled by the boiler, such as 24V or 120 VAC, for example.

Wiring the Circuit

As indicated in the wiring diagram, the power terminals (7 and 8) of the general-purpose 8-pin relay are directly connected to the boiler through the 120V supply (Phase and Neutral).

The Normally Closed (NC) terminal (1) of the relay is connected to the Normally Closed (5) terminal of the AH3-3 timer. The NC terminal (2) of the relay is connected to the Phase terminal (2) and the COM (8) terminal of the AH3 timer.

The COM (5) terminal of the relay is wired to the Normally Open (4) terminal of the relay and the 120V exhaust fan.

The rest of the circuit is powered by a 120V AC supply using a three-pin plug. Specifically, the Common (6) terminal of the relay is connected to the Phase wire, and the terminal (7) of the timer and the fan is connected to the Neutral wire.

Click image to enlarge

Working of the Circuit

1. When the overall circuit is connected to the 120V AC supply, the boiler turns on, causing the general-purpose relay to energize and activate the AH3-3 timer. Consequently, the fan starts running.
2. When the power supply disconnects, both the boiler and the relay turn off.
3. The AH3-3 timer activates, and the delay countdown begins.
4. During this time period, the fan continues to run.
5. When the predefined time expires, the fan turns off automatically. Therefore, the off-delay mechanism is successfully achieved.

The ratings of the circuit are:

• Max load = 720W
• Max loads for Motors = 1/4 hp
• 6A at 120V AC
• 3A at 240V AC
• Delay Time = 0-60 Mins

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