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D- OPTIONAL ELECTRIC HEAT
See ELECTRICAL / ELECTRIC HEAT DATA and ELEC
TRIC HEAT CAPACITIES (table of contents) for LCH to
EHA match-ups and electrical ratings.
EHA parts arrangement is shown in figures 15 and 16. All
electric heat sections consist of electric heating elements
exposed directly to the air stream. Two electric heat sec
tions (first section and second section) are used in all 15kW
through 90kW heaters. See figure 14. Multiple‐stage ele
ments are sequenced on and off in response to thermostat
demand.
FIGURE 14
HEAT SECTION PLACEMENT
FIRST ELECTRIC
HEAT SECTION
(LEFT SIDE)
SECOND ELECTRIC
HEAT SECTION
(RIGHT SIDE)
COMPRESSOR
COMPARTMENT
1-Main Control Box Components A55, K9
The main control box (see figure 3) houses the A55
Unit Controller and the K9 electric heat relay.
2-Contactors K15, K16, K17 and K18
Contactors K15, K16, K17 and K18 are all three‐pole
double‐break contactors located on the electric heat
vestibule. K15 and K16 are located on the first electric
heat section, while K17 and K18 are located on the sec
ond electric heat section. However, in the 15 and 30kW
heaters, the first section houses all contactors and fus
es. All contactors are equipped with a 24VAC coil. The
coils in the K15, K16, K17 and K18 contactors are ener
gized by the main panel A55. Contactors K15 and K17
energize the first stage heating elements, while K16
and K18 energize the second stage heating elements.
3-High Temperature Limits S15 and S107 (Primary)
S15 and S107 are SPST N.C. auto‐reset thermostats
located on the back panel of the electric heat section
below the heating elements. S15 is the high tempera
ture limit for the first electric heat section, while S107 is
the high temperature limit for the second electric heat
section. Both thermostats are identical and are wired to
the A55 Unit Controller. When either S15 or S107
opens, indicating a problem in the system, contactor
K15 is de‐energized. When K15 is de‐energized, first
stage and all subsequent stages of heat are de‐ener
gized. The thermostats used on EHA360‐45‐1 Y/G/J
are factory set to open at 200_F +
5_F (93.3_C + 2.8_C)
on a temperature rise and automatically reset at 160_F
+ 6_F (71.1_C + 3.3_C) on a temperature fall. All other
electric heat section thermostats are factory set to
open at 170_F + 5_F (76.7_C + 2.8_C) on a tempera
ture rise and automatically reset at 130_F +
6_F
(54.4_C +
3.3_C) on a temperature fall. The ther
mostats are not adjustable.
4-Terminal Strip TB3
Electric heat line voltage connections are made to ter
minal strip TB3 (or a fuse block on some models) locat
ed in the upper left corner of the electric heat vestibule.
5-Heating Elements HE1 through HE14
Heating elements are composed of helix wound bare
nichrome wire exposed directly to the air stream.
Three elements are connected in a three‐phase ar
rangement. The elements in 208/230V units are con
nected in a “Delta” arrangement. Elements in 460 and
575V units are connected in “Wye” arrangement.
Each stage is energized independently by the corre
sponding contactors located on the electric heat
vestibule panel. Once energized, heat transfer is in
stantaneous. High temperature protection is provided
by primary and redundant high temperature limits and
overcurrent protection is provided by fuses.
6-Fuse F3
Fuse F3 are housed in a fuse block which holds three
fuses. Each F3 fuse is connected in series with each
leg of electric heat. Figures 15 and 16 and table 6
shows the fuses used with each electric heat section.
For simplicity, the service manual labels the fuses F3
- 1 through F3 - 8.
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