Heathkit GD 1776 Schematic

Page 1

TO

URNACE

fiifiaafiumnixxTw

CIRCUIT DESCRIPTION

Refer to the schematic diagram below as you read the
following description.

Typically, a thermostat operates furnace controls on a
single AC circuit. The Programmable Home Heating
Control provides two circuits and a relay to operate
the furnace controls. in both switch positions. Econ or
Norm, the thermostat operates the rela}' which turns
the furnace on and off.

The Econ circuit provides a variable heater [lamlo]

- that raises the ambient temperature near the thermo-

stat at the programmed times by a preset amount.
When either the NormlEcon switch or Timer switch is

open, the heater circuit is turned off, and there is no
setback.

The Norm. or main circuit. half-cycle flows from the
transformer through the thermostat contacts. an-
ticipator. a steering diode, load, diode D2, and back to
the transformer. Load resistor R1 simulates the pri-
mary control current for prop er anticipator operation.
The voltage drop across the load activates the relay
which operates the furnace controls. Diode D1 and
capacitor Ci filter the circuit to prevent relay chatter.

The Econ circuit half-cycle provides a path from the
transformer through diode D3, the timer-controlled
switch, setback control R2, [he NORlVlfECON switch.
a "heater" lamp, a thermostat steering diode. and
back to the transformer.

SCHEMATIC OF THE

HEATHKIT®
PROGRAMMABLE HOME HEATING CONTROL

MODEL 60-1776

-u-u-n-nP---------------
ANTICIPATOR

@-H-'r-(L

THEN.
CONTACT

.5. ....________..

2162

®

SUB-BASE

THERMOSTAT

-_--- - ----'
h-----------