(i) Check for the possibility of leaking of refrigerant.

(ii) Check for loose or worn drive belts.

(iii) Improve internal operating pressure in the system.

(iv) A filter should be checked once a month to see if it needs cleaning or replacing. Remove filter & hold to a bright light, then try to look through it if you can see the light easily.


(v) outside mounted condensing unit-it should be cleaned of accumulated especially near inlet &outlet discharge grills, use a brush or hose, cleanout leaves & windblown dart or dust.

(vi) Use a vacuum cleaner once a month to clean off the louvers and once a year remove them entirely so that you can clean of the back of the louver as well as the inside of the ducts as far as you can reach easily.

Central air Conditioning advantages:

(a) Low in initial cost.


(b) Equipment can be located away from the space to be air conditioned.

(c) Low maintenance cost

(d) Exhaust air can be reused

(e) Less vibration.


(C) According to season in which air conditioning is used:

(a) Summer:

Net sensible heat gain. Reduction of water vapour. Net Latent heat gain, dehumidification.

(b) Winter:


Sensible heat gain, direct solar heat through glasses. Internal occupancy & appliances. Sensible & latent heat loss. Sensible heat loss through walls & glasses. Heat the air by heating coil.

(c) Year round:

Individual difference. Human comfort, moisture. Supply of oxygen distribution. Removal of Co, Sited at rest in still air generally 101 K cal/hr 21.1°C 50% R H, 85 m2/person/hr. 3-5 times per 1 hour. Air movement.

Air Conditioning Systems:


(A) Direct expansion system

(B) All water system

(C) All air system

(D) Air water system- heat pump


(A) Direct Expansion System:

Unit is placed vertically, water is cooled in a cooling tow -r. The liquid refrigerant from condenser flows directly to a thermostatic ex­pansion valve. After expansion valve refrigerant passes through distributors to evaporator coils, where cooling effect is produced.

Air Conditioners:

Air conditioners are mechanical ventilators of improved type. In such units provisions are made for treating the air so as to control simultaneously its temperature, humidity, purity and distribution to meet the requirements of the conditioned space.

Air conditioners may be centrally operated units, packaged air conditioners or room air conditioners and may be installed as required according to situation

(I) Room Air Conditioner:

The cooling coil fan sucks through a filter the warm room air & cools it by passing it over the cooling coil. (Evaporator), where it is cooled and dehumidi­fied and circulated back into the room.

Liquid refrigerant collects in the lower coils of the condenser and flows through the capillary tube refrigerant control into the evaporator coil. When the unit is in operation, this is under low pressure. The liquid refrigerant boils and picks up heat from the evaporator surface.

Low pressure vapour draws from the evaporator through the suction line & sent to the compressor where it is com­pressed to the high side pressure and forced into the condenser where it cooled and condensed to a liquid. This cycle is then repeated.

An adjustable thermostat mounted on the control panel with an On and Off switch provides the necessary control.

The compressor and condenser are mounted in such a way that the fan in the compressor condenser compartment draws outdoor air, circulates over the con­denser coil and discharges it outside.

Moisture which collects on the evaporator coils is collected in a drip pan under the coils. In some machines it flows into a pan in compressor compartment where in evaporating it, aids in cooling the compressor and condenser.

The only parts that can be serviced in the field are the relay control switch, fan motor starting and running capacitors, filters, and cabin parts.

Now a days split air conditioning system are available 1, 1.5, 2 T capacity.

(II) Package (Console) Air Conditioner:

Rectangular box with supply and return connection on the front and provi­sion for the condensing unit on the back side.

The Unit Is Divided Into:


Evaporator, condenser, expansion valve, compressor and control panel.

Air conditioning section:

Cooling/heating coil, inlet grill with filter and damper.

Air distribution section:

Blower, motor and outlet grill, automatic tem­perature control is provided with thermostat.


During air conditioning heating coils are operated which are electrically heated and air discharging over the coils, heated and then mixes with the pre circulated air to deliver the required conditioned air. Through humidifier air is supplied to the room.

Blower with motor, receiver and air discharge grill are provided at the top.

Blowers are used for supplying large quantities of air at relatively low pressure.

Air conditioner selection is based on:

(a) Size of the room

(b) Roofing/ceiling height – heat gain

(c) Number of persons.

(d) Wall construction

(e) Area of outside wall which is covered with glass

(f) Duty – Exposure to the sun, wattage of lamp, TV etc.

Maintaining Room Air conditioner:

I. Dry the grill & condenser coil.

Use a soft brush & a vacuum to remove dust & lint wiper off the louvers or grills.

II. Bent grills should be straightened.

III. Fan blade – dust & lint.

Wiped off with a soft cloth.

IV. Scrape – off with little fine steel wool, wipe off the dust touch up the base metal with a rust resistant metal provided.

(B) All Water System (Chilled Water):

Water is chilled in water chillers of the refrigeration unit. The chilled water is pumped to different rooms. Each room has its own fan coil unit. In these fan coil units, air is sucked from the room and cooled by chilled water and thus cooled air is circulated in the rooms.

Each fan coil unit has outdoor air intake, return air intake filter, dehumidifier, fan and air outlet. The refrigeration plant may be installed remotely, two/three/four pipe system.

Boilers are used for supplying steam in winter for heating.

There is no duct work. Individual control of each room is much better.

(C) All Air System :

Central station systems are conventional all air systems. Central station employs air handling and refrigeration units. The air handling equipments in­cludes the fan, filter, Heater, cooling coil, dampers for control of air volume and distribution system of ducts or conduits.

The refrigeration equipments consisting of one or several machines usually are centrally located and several air handling units may be served from central refrigeration plant.

Control temperature, humidity and air quality in the conditioned space is provided by various types of air terminals.

Proper ducts are laid for supply and return of air. Cleanness must be maintained throughout the air conditioning system.

Tightness is important to avoid loss of oil and refrigerant and to prevent entrance of water, air and other non condensable gases.

Motor, dampers etc. should be lubricated regularly.

All safety devices should be kept operative,

(D) Air Water System :

Air is delivered either to coil units or directly to the room through. Corridor duct system & separate outlets. Outdoor air intake, preheated, filter & optionally heater & humidifier.

For air quality filtering humidity fresher’s small quantity centrally condi­tioned air stream equal to the total fresh air is provided.

I. Induction system. If the water distribution provides either heating or cooling only it is called two pipe systems. If it provides simultaneous heating & cooling, it i.e. either 3 or four pipe system.

II. Fan coil with supplementary air.

III. Radiant panel with supplementary air.