40 Component Operation and Maintenance
6.2 Filters
Filters are usually the most neglected item in an environmental control system. To maintain efficient
operation, they should be checked monthly and changed as required. Because replacement intervals
vary with environmental condition and filter type, each unit is equipped with a filter clog switch. This
warns of restricted airflow through the filter compartment by activating the Change Filter alarm.
Turn the power off before replacing filters.
Himod filters are 20" by 20" by 4" thick. The filter is replaced from the front of the unit. First remove
the t-strip gaskets. Starting with the filters on the right side, slide the filter up and outward toward
you to remove it. Continue removing the other filters by sliding them to the right, then slide each up
and outward.
After replacing the filters and the t-strips in reverse order, test the operation of the filter clog switch.
Turn the adjusting screw counterclockwise to trip the switch—this will energize the Change Filter
alarm. To adjust the switch, proceed as follows: With the fan running, set the switch to energize the
light with clean filters. The unit panels must all be in place and closed to accurately find this point.
Then turn the adjusting knob one turn clockwise or to the desired filter change point.
6.3 Motor Section
6.3.1 Fans
The fan should be checked monthly to verify that the blower wheel rotates freely without any abnor-
mal noise. Amp draw to each motor should also be checked for each motor. Section 6.0-6.6 of the
Installation Manual may be consulted for field air volume and/or external static pressure adjustment
details.
6.4 Refrigeration System
Each month, the components of the refrigeration system should be inspected for proper function and
signs of wear. Since, in most cases, evidence of malfunction is present prior to component failure, peri-
odic inspections can be a major factor in the prevention of most system failures.
Refrigerant lines must be properly supported and not allowed to vibrate against ceilings, floors or the
unit frame. Inspect all refrigerant lines every six months for signs of wear and proper support. Also
inspect capillary and equalizer lines from the expansion valve and support as necessary.
Each air cooled unit liquid line has a sight glass that indicates liquid refrigerant flow and the pres-
ence of moisture. Bubbles in the sight glass indicate a shortage of refrigerant or a restriction in the
liquid line. The moisture indicator changes from green to yellow when moisture is present in the sys-
tem.
Glycol cooled units do not have a sight glass or moisture indicator. They are critically charged. Liquid
subcooling and suction superheat are good indicators of correct charge (see 6.4.4 - Thermostatic
Expansion Valve and 6.4.7 - Glycol Cooled Condensers).
Check compressor current during maintenance. Check also for unusual noise in compressor. Verify
that there is no ice formation on the evaporator.
NOTE
Section 6.3 of the Installation Manual may be consulted for high efficiency filter pressure drop
information.
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