McQuay MWM Service Manual Book page 61

ii ) Diagnosis of Refrigerant Circuit / Application
There might be some causes where the unit starts running but does not perform
satisfactorily, i.e. insufficient cooling. Judgement could be made by measuring temperature
difference of indoor unit's intake and discharge air as well as running current.
Insufficient cooling
Restricted
Air
circulation
High cooling
load
Refrigerant
circuit
Compressor
Satisfactory operation with temperature difference of air
intake & discharge of indoor unit 8°C to 13°C. *
( * value is for reference only )
: Faulty
Indoor / outdoor coil dirty
(clogged)
Indoor air filter dirty
Fan motor malfunction
Obstruction at air inlet /
outlet of indoor / outdoor
unit
Excessive heat source.
e.g. electric kettle
Room overcrowded with
people
Windows / doors wide
open
Refrigerant short charge
or refrigerant leakage
Restriction e.g. at
strainer, capillary, filter
dryer, etc.
Less or no compression
(Low running current)
Check Cause
: :
Remedy
:
Clean the coil
Clean the filter
Change or repair
the motor
Remove the
obstruction
Remove or reduce
heat source
Reduce number
of people in the room
Close the
windows / doors
Add refrigerant.
Repair leakage
if detected
Repair clogging
or replace faulty
components
Replace compressor
60