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1F90 and 1F97  
Addendum to  
WHITE-RODGERS  
INSTALLATION INSTRUCTIONS  
FAILURE TO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY  
BEFORE INSTALLING OR OPERATING THIS CONTROL COULD CAUSE  
PERSONAL INJURY AND/OR PROPERTY DAMAGE.  
PRECAUTIONS  
Ifindoubtaboutwhetheryourwiringismillivolt,line,orlow  
voltage, have it inspected by a qualified heating and air  
conditioning contractor, electrician, or someone familiar  
with basic electricity and wiring.  
CAUTION  
!
To prevent electrical shock and/or equipment  
damage, disconnect electric power to system, at  
main fuse or circuit breaker box, until installa-  
tion is complete.  
Do not exceed the specification ratings.  
All wiring must conform to local and national electrical  
codes and ordinances.  
Do not short out terminals on gas valve or pri-  
marycontroltotest.Shortorincorrectwiringwill  
burn out thermostat and could cause personal  
injury and/or property damage.  
INSTALLATION  
WHENTHISTHERMOSTATISCONNECTEDTOSOME If you observe any or all of these conditions after installing  
SYSTEMSTHATUSEHIGHIMPEDANCEINPUTELEC- thermostat,youcancorrectsystemoperationbyinstalling  
TRONIC MODULES, YOU MAY OBSERVE THE FOL- isolationrelaysbetweenthethermostatandtheelectronic  
LOWING CONDITIONS.  
ignition module. Figures 1 and 2 show how three isolation  
relays can be installed [one each for the fan (G), heat (W),  
andcool(Y)].Youmaynotneedtoinstallallthreeisolation  
relays to correct the operation conditions.  
1. The furnace fan may turn on when heat has not been  
called, ormaynotturnoffwhenthermostatissatisfied  
and call for heat ends.  
2. The furnace may not turn off when thermostat is  
satisfied and call for heat ends.  
3. The air conditioner may not turn off when thermostat  
is satisfied and call for cool ends.  
Figure 1 shows a single transformer heating/cooling sys-  
tem, with isolation relays installed in the heating (W),  
cooling (Y), and fan (G) circuits. To simplify the diagram,  
limit and safety switches are not shown here, although  
they will be found either in the low or high voltage circuit.  
Limit and safety switches must be retained. Refer to the  
equipment manufacturer’s system wiring diagram for the  
location of limit and safety switches.  
THERMOSTAT  
Red Jumper Wire  
RH  
W
Y
G
RC  
Line  
Voltage  
24 VAC  
WARNING  
!
Heating Cooling  
System System  
Fan  
Relay  
Transformer  
DO NOT REMOVE OR WIRE AROUND LIMIT AND  
SAFETY SWITCHES WHEN INSTALLING ISOLA-  
TION RELAYS.  
Figure 1. Wiring for single transformer systems  
WHITE-RODGERS DIVISION  
EMERSON ELECTRIC CO.  
9797 REAVIS ROAD  
ST. LOUIS, MISSOURI 63123-5398  
PART NO. 37-5426A  
Printed in U.S.A.  
9507  
R
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INSTALLATION (cont’d)  
THERMOSTAT  
RH  
W
Y
G
RC  
Line  
Voltage  
Line  
Voltage  
24 VAC  
24 VAC  
Heating Cooling  
System System  
Fan  
Relay  
Transformer  
Transformer  
Figure 2. Wiring for two-transformer systems  
Figure 2 shows a two-transformer heating/cooling sys-  
tem, with isolation relays installed in the heating (W),  
cooling (Y), and fan (G) circuits. To simplify the diagram,  
limit and safety switches are not shown here, although  
theyarefoundeitherintheloworhighvoltagecircuit.Limit  
and safety switches must be retained. Refer to the  
equipment manufacturer’s system wiring diagram for the  
location of limit and safety switches.  
WARNING  
DO NOT REMOVE OR WIRE AROUND LIMIT AND  
SAFETY SWITCHES WHEN INSTALLING ISOLA-  
TION RELAYS.  
!