Control Relay for Arilaire 700 Series Two

Control Relay for Aprilaire 700 Series Two

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Control Relay for Model 700A 700M

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Part Number: 4740

Quantity

Description

Series One

Series Two

4740
4238

Aprilaire 4740 relay for the new Model 700 Series Two. This controller mounts on the motor board bridge (RP-4243). Mounting holes are spaced 1½".

Note: the new Aprilaire 700 Series are wired different than the earlier model 700. In Dec 2007 Aprilaire revised the 700 by removing the internal 24vac transformer. The new 700 700A 700M now require an external 24vac supply.

This relay control is different than the control board that was used in the earlier 700 model. The earlier 700 control board had an on-board 24vac transformer.

Aprilaire 700 Series Two Wiring - 2008 to Present

The Aprilaire model 700A, 700M and 700 manufactured in 2008 and later are Series Two and designed primarily for an automatic humidistat. To turn-on these units require a humidistat that sends 24v to the humidifier.
Aprilaire 700 Series 2 Wiring
The 700 series two has a controller relay (pn 4740) that turns on the fan when the humidistat sends 24v to the humidifier. The 24v is also routed to the solenoid valve. The diagram above shows the operation of this controller relay.

The operation of the series two controller relay is significantly different than that in the previous model 700. For simplicity the above diagram does not show the wiring to the humidistat necessary to sense when the furnace is running. Or the outdoor temperature sensor.

Aprilaire 700 Series One Wiring - Through 2008

The Aprilaire model 760, 768 and 700 manufactured before 2008 were Series One and originally designed for a manual humidistat. To turn-on the unit required a simple on-off switch type humidistat. An automatic humidistat was retrofitted.
Aprilaire 700 Series 1 Wiring
The 700 series one has a controller board (pn 4238) with a 24v transformer that powers the fan relay and solenoid valve. The diagram above shows the operation of this controller board.

The operation of the series one controller board is significantly different than that in the current model 700. For simplicity the above diagram does not show the wiring necessary to supply 120v only when the furnace is running. Or otherwise the addition of the model 50 current sensing relay.

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Control Relay for Aprilaire 700 Series Two

Aprilaire 700 Series Two Wiring - 2008 to Present

Aprilaire 700 Series One Wiring - Through 2008

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