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Equipment Interface Module
The W8635A Equipment Interface Module (EIM) pro-
vides 24 Vac control of single or multistage conventional
HVAC equipment when used with a T8635L Microelec-
tronic Communicating Programmable Thermostat. The
W8635A can be used with up to 2 heat/2 cool conven-
tional applications. See Table 1.
Table 1. Description.
When Installing this Product…
Read these instructions carefully. Failure to follow
these instructions can damage the product or
cause a hazardous condition.
Check the ratings given in the instructions and on
the product to make sure the product is suitable for
Installer must be a trained, experienced service
After completing installation, use these instructions
to check out the product operation.
Can cause electrical shock or equipment
Disconnect power before supply before beginning
Mounting Location Hazard.
Mounting W8635A inside HVAC equipment
can damage the EIM.
Mount the W8635A only on the outside of HVAC
Locate the W8635A in the equipment room near
the HVAC equipment. See Fig. 1.
Fig. 1. Selecting W8635A Equipment
Interface Module location.
Remove the cover from the W8635A by pulling on
the edge of the module.
Locate the two mounting holes. See Fig. 2.
Model Application Stages Terminals Comments
W8635A Conventional gas, oil
or electric heat
Up to 2 heat/
1, 2, 3, C, R, Rh, Rc,
G, W1, W2, Y1, Y2
Use with T8635L Communicating
FURNACE OR BOILER