AAON M1-011 - Manual (Page 28)

28
Figure 7.3, Belt Deflection
Coils
Coils should be inspected and cleaned annually to
ensure there is no obstruction to airflow.
Evaporator (Indoor/Cooling Coil)
Dirty evaporator coils will eventually freeze up, and
often result in a time consuming, and expensive
service call. Clean filters will help to prevent dirt from
accumulating on the evaporator, however the
evaporator should be cleaned annually with a soft
bristled brush, and/or a non-corrosive coil cleaning
solution.
Condenser (Outdoor Coil)
One of the most overlooked maintenance
requirements is the need to keep air moving freely
across air-cooled condensing coils. Dirty condensers,
like evaporators, can significantly increase cooling
costs during the year. As a minimum, clean the
condenser coil at the beginning of each cooling
season. It is preferable to use a medium pressure
water spray from the inside of the condenser cabinet
with a non-corrosive coil cleaning solution. TURN
OFF all power to the unit before cleaning.
Comb out any visible exterior fin damage to help
maintain unit efficiency. Clean the fan blades if they
are dirty. Always check condenser fan blades to
ensure unobstructed, free rotation after manipulating
the unit cabinet in any way, and before turning power
back on to the condenser.
Refrigeration Cycle
Satisfactory performance of the refrigeration cycle can
be determined by measuring suction line superheat.
In order to determine if refrigerant flowing from the
evaporator is dry, ensure that the system has enough
refrigerant to produce liquid line subcooling, but not so
much to cause abnormally high condensing
temperatures (and pressures). Refrigerant cycle
analysis is best performed in conditions that approach
the conditions where the air conditioner will be
expected to operate.
Superheat
Superheat is the extra heat in vapor when at a
temperature higher than the saturation temperature
corresponding to its pressure. To determine the
superheat, measure the temperature of the suction line
(insulate the temperature probe from surrounding air),
and read the suction line pressure. The difference
between the suction line temperature, and the
temperature indicated on a refrigerant pressure-
temperature chart (see inside back cover) at the
suction line pressure is the degree of superheat.
Subcooling
Subcooling enhances unit capacity, and assures that
only liquid appears at the threshold of the expansion
valve, also prolonging expansion valve life, and
providing better expansion valve control. Subcooling
is determined by measuring the difference between
the temperature of liquid refrigerant as it leaves the
condenser coil, and the temperature indicated on a
pressure-temperature chart at the pressure measured
in the liquid line.
Determining Charge
Table 7.2 shows expected discharge superheat levels
in R-22 systems when properly charged. To
determine proper charge using this table, do the
following:
1. Connect manifold gauges to the unit, and allow the
unit to operate for at least 5 minutes in order to
allow system pressures to stabilize.
2. Attach thermocouples to discharge line, and take
temperature measurement.
3. Measure suction, and discharge pressures, and
convert to saturated temperatures using the
temperature-pressure chart.
4. Subtract saturated condensing temperature from
measured discharge line temperature to get
discharge line superheat.
Sheave Centers
Force
Deflection = 1/64 th in.
per inch of length