Install Instructions

X-XX UL
INSTALLATION INSTRUCTIONS
®U.S. Registered Trademark
Copyright © 1996 Honeywell Inc. • All Rights Reserved
ST74A1053
Defrost Controller
APPLICATION
The ST74A is a low voltage time/temperature electronic
defrost controller for heat pumps. This device provides
timed low voltage relay switching to control an external
heat pump defrost relay.
A complete list of the specific Honeywell and other
controllers that the ST74A Defrost Controller is designed
to replace is provided in Tables 1 and 2.
Table 1. OEM Replacement Part Numbers.
INSTALLATION
When Installing this Product…
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazard-
ous condition.
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable for
your application.
3. Installer must be a trained, experienced service
technician.
4. After installation is complete, check out product
operation as provided in these instructions.
CAUTION
Disconnect power supply before beginning
installation to prevent electrical shock or equipment
damage.
Mounting
Mount the ST74A in the wiring compartment of the outside
section of the heat pump. Use the ST74A as a template to
mark the position of the four mounting eyelets. Use No. 6
or No. 8 sheetmetal screws in the four mounting eyelets.
The control can be mounted in any position,
+ 45 degrees
to vertical.
Wiring
Disconnect power supply to prevent electrical shock or
equipment damage. All wiring must comply with local
codes and ordinances. Refer to Fig. 1 for wiring hookup.
The Off cycle time is determined by a selectable jumper
that allows a choice of 50, 70, or 90 minutes when
connected to T1, T2, or T3, respectively. Select the timing
that is closest to the timing of your original control. If the
timing does not exactly match, choose a longer timing
rather than a shorter one.
See Table 3 for a description of the terminal functions.
Manufacturer Service Part Number
Amana C64301-1
C6431001
Artesian 10321-00
Arcoaire 32312-00
Carrier 621
Coleman 3030A374
Goodman B12260-06
Heil Quaker HQ1052757
ICP 1052757
Intertherm 6208800
Lennox 33G9501
Rheem 47-21776-01
SnyderGeneral 1395-329
Table 2. Controller Manufacturer
Replacement Part Numbers.
69-0990-1
Manufacturer Part Number
Honeywell ST74A 1004
ST74A 1020
ST74A 1038
White-Rodgers/Steveco 90-621
ICM 300C
Therm-o-Disc 26E-10
Robertshaw TD-10