A & T International 1 Service Manual page 19

Power Supply Check
• Verify proper field voltage and breaker size with rating
plate.
• Use voltmeter to verify incoming power supply agrees
with rating plate. Incoming power should not exceed
nameplate voltage. Incoming power should not be
below minimum voltage stated on rating plate (197V
for units rated 208/230V and 104V for units rated
115V).
• Check low voltage power. Place voltmeter across low
Volt terminals "R" and "C" at indoor unit, reading
should be 24V.
Test Mode
Test mode is available only on units with unit mounted
controls. Test mode feature aids in functional check of the
unit. Use to help isolate a problem source.
NOTICE
While in test mode, all timers are eliminated.
After system checks are complete, control shall
be returned to normal operation. DO NOT LEAVE
SYSTEM IN TEST MODE!
To enter test mode place unit in off state.
Use unit mounted keypad. Depress both up and down
arrow buttons simultaneously and push On/Off button in
for one second. Unit is now in test mode. System function
checks can now be made without having to wait for timer
delays.
To return to normal operation, switch unit off again via
On/Off button for at least 30 seconds. When system is
switched back on, normal operation will resume.
Cooling Only Units
Cooling only units utilize low Volt interconnecting wires
between indoor unit and thermostat.
Air handlers with unit mounted controls, wires (WCP) or
terminals (CCP) designated "Y" (yellow) and "C" (brown) of
indoor air handler should be connected to corresponding "Y"
(yellow) and "C" (brown) wires or terminals.
Other wires or terminals such as "R"(red) or "O" (orange)
may not be needed. Protect unused terminals by use of wire
nut from making contact with junction box or other metal
surfaces.
Refer to low volt interconnect diagram interconnect diagram
Figure 1 for unit mounted controls and Figure 2 for remote
thermostat connection.
TROUBLESHOOTING PROCEDURE CONTINUED
24V transformer located in indoor air handler unit provides
low Volt control power to indoor air handler.
24V power supply can be measured by placing meter
across "R" and "C" low Volt terminals. Air handler will
switch on and off cooling through yellow (Y) wire. When
air handler is calling for cooling, 24V can be measured
between terminals (wires) Y and C.
Electric Heat
Units with electric heat utilize control relay located on
circuit board in control box. As safety feature, auto reset
limit switch located on heater end plate or on heater
assembly interrupts power to the heater should an over-
heat condition occur.
Each electric heat assembly is also equipped with a one
time fuse link. Should electric heat temperatures rise above
auto reset limit switch, a non-reset, one time fuse link will
open and heater will remain off.
Following current values apply when unit is connected
to 230V power supply. These values include fan motor
current. If supply power is different, amp draw of heater is
affected.
5kw = 22.3 amps
4kw = 18 amps
3kw = 13.5 amps
Units With Optional Condensate Pumps
EMI Air Handlers are available with optional condensate
pump. Condensate pumps are recommended when it is
not possible to gravity drain condensate from indoor unit.
Depending on pump manufacture the maximum lift for
pump will vary. Consult pump instructions for maximum lift
for pump being used.
Condensate generated by air handler will collect in pumps'
reservoir. When water level is high enough, float switch
closes and energizes pump motor clearing water from
the reservoir. Should water exceed maximum preset
level, safety switch will open, interrupting (Y) signal. This
prevents air handler from generating more condensate and
spilling out of unit.
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