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Marvair Classic AVHA Heat Pump I&O Manual
08/2018 Rev. 2
SPECIAL NOTES FOR UNIT INSTALLATION
1. Minimum 12” clearance at the bottom of the unit for
unrestricted airflow
2. Ensure the ambient temperature uniformity around unit
3. Intake and discharge of the outdoor air flow must not be
restricted or altered
4. All insulation and sealing related to the installation must
be completed properly
5. External Static pressure should not exceed the minimum
value in the AHRI Standard 390
INSTALLATION (K: CONDENSATE DRAIN)
A 3/4” drain hose is located on the bottom side of the unit. The
drain may be extended for condensate removal to comply with
local codes (use fitting size or larger). Install a condensate
trap on this line.
INSTALLATION (L: OPTIONS)
Marvair wallmount air conditioners and heat pumps have the
ability to equip a variety of options:
•
Electric Heat 5-20kW
•
Sound Attenuation Module
•
Powered Ventilation Damper
•
Low Ambient Packages
•
Economizer
•
Lead Lag Controllers
Option kits must be installed according to the respective
installation manual to ensure safe and reliable operation.
Installation manuals are included with the option kit or can be
found on the Marvair website, www.marvair.com.
INSTALLATION (M: SEQUENCE OF OPERATION)
COOLING MODE
Low-voltage thermostat terminal R is connected to Y, O, and
G, at the unit low-voltage terminal board.
The system reversing valve is energized during the cooling
mode. Power is supplied to the reversing valve solenoid
through the low-voltage O terminal. The low-voltage Y terminal
to the control will energize the contactor latch coil (causing
the contactor to energize the compressor). The low-voltage
Y terminal to the control will also energize the control’s timer.
During the cooling mode, the defrost thermostat is open (coil
temperature is above 30°F) and will not allow the time to be
accumulated to initiate the defrost mode. The outdoor fan is
wired through the N/C points of the control’s relay and the
N/O points of the contactor. The fan motor will be energized
whenever the contactor is energized (except during defrost).
HEATING MODE
Low-voltage terminal R is connected to Y and G, at the unit
low-voltage terminal board.
The system reversing valve is not powered during the heating
mode. With the thermostat system switch turned to heat. The
Y terminal will energize the compressor, outdoor fan, and the
indoor blower.
DEFROST MODE
To prevent ice build-up on the coil during the heating mode, as
the outdoor coil temperature falls below 30°F ±5°F, an outdoor
defrost thermostat closes. (This thermostat is located on a coil
tube.) When the thermostat closes, the timer on the defrost
control starts accumulating the compressor run time. After the
selected time (30, 60,or 90 minutes) has been accumulated,
the controller will start the defrost cycle regardless of the
outside temperature. During the defrost cycle, the system
is switched back into the cooling mode by the control de-
energizing the reversing valve solenoid. The N/C pole of the
control fan relay is opened, turning off the outdoor fan to allow
the outdoor coil to be warmed (defrosted) faster. The defrost
control energizes the indoor auxiliary heat relays through the
E terminal to temper the indoor supply air. This terminal should
be connected to E (second-stage heat) on the thermostat.
After the defrost thermostat reaches 65°F ±5°F, the defrost
cycle will end. The control will not allow the defrost to continue
longer than 10 minutes.
DEFROST TIME SELECTION
The defrost control has three selectable time intervals: 30, 60
and 90 minutes. The timing is factory set at 60 minutes. This
timing has been determined by testing to provide the best
operating efficiency. In areas where the humidity is lower than
normal, the timer may be set to a higher time (90 minutes). To
change the time, move the timer jumper to the postmarked
30 for 30 minutes, 60 for 60 minutes, or 90 for 90 minutes.
DEFROST TEST POST
The defrost control has test posts to speed up the defrost time
setting by a factor of 256.
If you want to initiate a defrost without waiting for the time to
accumulate, you can jumper the two test pins (marked test).
If the coil temperature is above 30°F you will need to jumper
the DFT (defrost thermostat) terminals to simulate a closed
thermostat. The defrost cycle should occur in 7 seconds for
a 30-minute setting, 14 seconds for a 60-minute setting, and
17 seconds for an 90-minute setting. If the jumper is removed
immediately when the defrost cycle starts, the cycle will end if
the defrost thermostat is opened (coil above 65°F). If the test
pins remain jumped, and the defrost thermostat is closed, the
defrost will end in 2.3 seconds, which is the 10-minute default.
DURING THE ABOVE TEST, DO NOT CONTACT OR SHORT
ANY OTHER PIN. THIS MAY DAMAGE THE CONTROL.
INSTALLATION (N: HIGH-PRESSURE LOCKOUT)
FIELD CHARGING
Compared to a cooling-only unit, a heat pump is difficult to
field charge correctly without the use of charging scales. It
is recommended the charge be weighed in with an accurate
charging scale. The correct charge weight can be found on
the unit name plate.
AVHA units may be equipped with a high-pressure switch.
This switch is wired through a lockout relay to lock out the
system if the high side pressure exceeds 650 psi. The high
side pressure MUST be below 450 psi before the system can
be reset.
