• Cooling is the transfer of heat from an area where it is not wanted to an area where it is not objectionable.

• Heat always flows from a warmer to a cooler area.

• "Ambient Air" is temperature of air surrounding an object (i.e. room temperature)

• There are three types of heating or cooling: conduction, convection and radiation.

• Insulation slows the rate of heat flow.

• Capacity of cooling systems is the heat removal rate produced and is measured in British Thermal Units (B.T.U.) per hour.

• A BTU is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

• One ton of cooling equals 12,000 BTU per hour, which equals the amount of heat required to melt one ton of ice in 24 hours (288,000 BTU).

• One Watt of electric energy equals 3.42 BTU. One horsepower equals 746 Watts equals 2,545 BTU.

• Air flow circulated in an area is expressed in cubic feet per minute (CFM).
• Air flow required to provide adequate heat or cool in an area is equal to 450 CFM per 12,000 BTU.
• Air flow required to provide adequate heat or cool in an area is equal to 450 CFM per 12,000 BTU.
• Warm air holds more moisture (water vapor or relative humidity) than cold air.
• Water vapor collects (condenses) on a cold surface.
• One gallon of water equals 8.3 lbs.
• One Foot Head equals 2.31 lbs. pressure.
• Water flow required to condense high pressure refrigerant gas equals 1.5 gal/min. at 75ºF water per 12,000 BTU and equals 3.0 gal/min. at 85ºF water per 12,000 BTU.
• Latent heat is heat added or removed that accomplishes a change of state: solid to liquid to vapor. Latent heat cannot be measured by a change in temperature.
• Water not under pressure will flow downhill.

Before starting up any Technicold air conditioning system, make sure that each of the below steps are followed. Failure to do so can lead to system failure that will not be covered by warranty:

• The cooling unit must be bolted securely into place.

Among the chief principals to know about the refrigeration cycle is that there are two pressures existing in a single compression system. The first is evaporating, or low pressure, and the second is condensing or high pressure.

The refrigerant acts as a transportation medium. It moves heat from the evaporator to the condenser where it is given off into the ambient air. In a water cooled system, the heat is given off into the cooling water. By changing its state from liquid to vapor and back to liquid, the
refrigerant absorbs and discharges large quantities of heat efficiently.

The basic refrigeration cycle follows this pattern:

• High pressure liquid refrigerant is fed from the receiver through the liquid line, and through the filter-drier to the metering device. (The metering device separates the high pressure side of the system from the
  low pressure evaporator). Various types of control devices may be used, but for purposes of this illustration, only the thermostatic expansion valve will be considered.

• The thermostatic expansion valve controls the feed of liquid
  refrigerant to the evaporator. By means of an orifice it reduces the pressure of the refrigerant to the evaporating or low side pressure.

• This reduction in pressure causes the liquid refrigerant to boil and vaporize until the refrigerant is at the saturation temperature that corresponds to its pressure. As the low temperature refrigerant passe through the evaporator coil, heat flows through the walls of the
  evaporator tubing to the refrigerant. This boiling action continues until the refrigerant is completely vaporized.

• The expansion valve regulates the flow through the evaporator as necessary to maintain a preset temperature difference or "superheat" between the evaporating refrigerant and the vapor leaving the evaporator. As the temperature of the gas leaving the evaporator varies,
  the expansion valve power element bulb senses the temperature, and acts to modulate the feed through the expansion valve.

• The refrigerant vapor leaving the evaporator travels through the suction line to the compressor inlet. This vapor is compressed to increase pressure and temperature. The hot, high pressure gas is forced out of the compressor discharge valve and into the condenser.

• As the high pressure gas passes through the condenser, it must be
  cooled externally. On air cooled systems, a fan, and fin-type condenser surface is normally used. On water cooled systems, a
  refrigerant-to-water heat exchanger is typical. As the temperature of
  the refrigerant vapor reaches the saturation temperature corresponding to the high pressure in the condenser, the vapor condenses into a liquid and flows back to the receiver to repeat the cycle.

• The refrigerant process is continuous as long as the compressor operates.

A common concern in marine air conditioning is excessive moisture in the cycling system. This can adversely affect the effectiveness of your AC system and can be noticed by the following symptoms:

• Holding plate sweats but will not freeze.
• Box temperature rises slowly.
• Compressor clutch will cut in and out with Ranco low pressure control connected to system.

If the drier has absorbed its capacity in moisture, the overflow can be released into the system at large. The moisture droplets can then freeze in the small orifice of the expansion valve. This can lead to the restricted flow of refrigerant to the holding plate.

To confirm the presence of excess moisture in your AC system, simply consult the indicator rings (or "stripes") on your system's sight glass. If the rings alternate in color between yellow and green, that indicates moisture in the system. If all rings are green, that indicates a dry system and the problem may be with a faulty expansion valve.

(On units equipped with a low pressure control, the unit will cut in and out if a "freeze-up" occurs. Because Freon is not returning to the compressor, the machine will shut itself down into a partial vacuum to below the setting on the low pressure control.)

To correcting the problem of excessive moisture, simply replace the drier. You should always carry a spare drier in your spares kit, along with several cans of R-12 refrigerant. In an emergency, if a new drier is not available, remove the old one and place it inside your oven. Bake the drier at 300 degrees F for two hours. Let the drier cool inside the oven then replace it back into the system. This is only a last ditch, short-term fix and the drier should be replaced as soon as possible.

CHECKING FOR LEAKS

Nothing contributes to long-term problems in a refrigeration system like leaks. A little preventative checking can save big issues down the road.

To check for leaks in your refrigeration or cooling system, first make sure that all flares and flare joints are correctly aligned and tightened properly. Remove all protective caps and install
refrigeration gauges on the suction and discharge service ports. Charge the system with Dry Nitrogen or a Nitrogen/Refrigerant gas mixture to at least 50 psig.

While the system is under pressure, you should quickly use liquid soap (i.e. Formula 409, Fantastic, etc.) on all fittings to locate all large leaks first. Doing this quickly is critical, to ensure that the
vicinity is not contaminated with refrigerant gas. When the larger leaks have been sealed, the system must now be tested for smaller leaks by using either an electronic leak detector or a halogen gas leak detector. Each and every fitting should be checked individually to
determine the systems integrity.

The soap solution should be cleaned off the flare joint upon completion of the leak check.

PURGING & EVACUATING

Another common maintenance issue on marine cooling systems, is purging and evacuating the nitrogen (or nitrogen/refrigerant mixture) from the pipes. An authorized factory dealer has the equipment and know-how to perform this procedure quickly and economically. However, if you must purge your cooling system yourself, do so with the utmost care and caution as the procedure involves exposure to potentially dangerous chemicals.

Always wear protective clothing and eye protection when relieving the system of pressure. The area to which it is being discharged should be well ventilated and there should be no open flames or hot surfaces. Many refrigerants can release Phosgene gas when exposed to a open flame or
decompose on a hot surface. Asphyxiation and death can occur if any gas is discharged into a confined space.

After the system has been purged it should be evacuated using a commercial refrigeration vacuum pump. The vacuum pump should be attached to both service ports and the service valves should be placed in the mid-seat position. The vacuum pump should be placed in operation for a
period of at least 20 minutes to remove moisture and non-condensable particles in the system. The system should be evacuated until a gauge reading of 30 inches Hg or 500 microns is achieved.

Once the required setting is achieved, close the discharge and suction gauge hand valves. Loosen the gauge manifold center hose connection from the vacuum pump to break the vacuum. Turn off the vacuum pump and remove the center hose connection. Connect the center hose to the refrigerant tank and open the valve on the tank. Crack open the center hose
connection at the manifold gauge body to purge out any non-condensable particles, then tighten once refrigerant is seen. The system is now ready for charging.

Any time a cooling system's compressor line starts - whether single phase or three phase - it draws a high starting current. This can be three to five times the Running Load Amps (RLA) of the compressor.

The ships' generator and shore power need to be sized to accommodate this surge. If the power supply is inadequate it can lead to such problems as tripped breakers, dimming lights or the generator set itself becoming "bogged down."

On three phase compressors, this issue can be alleviated with a Variable Frequency Drive (VFD). The VFD ramps up the frequency, voltage and current from zero to their maximum settings over a preset time period. This eliminates the starting surge when the compressor is required to
operate. The input voltage to the drive can be single or three phase but the output will always be three phase.

The variable drive is composed of four major parts: An input diode bridge and filter, a power board, a control board, and an output intelligent power module.

The basic principle:
AC power goes into the drive and is converted to DC power. This DC power is filtered to clean it up and smooth it out. It is then electronically converted back over to AC power and fed to three outputs.

The technical description:
Incoming AC line voltage is converted to a pulsing DC voltage by the input diode bridge. The DC voltage is supplied to the bus filter capacitors through a charge circuit which limits inrush current to the capacitors during power-up. The pulsating DC voltage is filtered by the bus capacitors which reduces the ripple level. The filtered DC voltage enters the inverter section of the drive, composed of six output intelligent insulated gate bi-polar transistors (IGBTs) which make up the three output legs of the drive. Each leg has one intelligent IGBT connected to the positive bus voltage and one connected to the negative bus voltage. Alternately switching on each leg, the intelligent IGBT
produces an alternating voltage on each of the corresponding motor windings. By switching each output intelligent IGBT at a very high frequency (known as the carrier frequency) for varying time intervals, the VFD is able to produce a smooth, three phase, sinusoidal output current wave which optimizes motor performance.

The input circuit of the VFD requires three voltage inputs (three phase) for correct operation and conditioning of the electronics and DC bus capacitors. When we only have two voltage inputs available (single phase) we connect them to the L1 and L2 of the VFD input terminals and place a jumper from the L2 terminal to the L3 terminal. This simulates a third leg of input power and the VFD operates correctly.

The installation and maintenance of refrigeration equipment is one of the most exacting and demanding tasks in the service field. Extreme care and craftsmanship must be taken when working with equipment built to the close tolerances and fine precision of marine cooling systems. Beyond the hardware of such a system, the chemical refrigerants that form the blood stream of marine cooling also demands scrupulous attention and care.

So long as a refrigerant is tightly contained and properly controlled, it can be made to perform useful work. But it doesn't do so willingly. Given the slightest opportunity, it will escape. If joined by such common substances as moisture or air, it combines with them to form
acids and attack the system. And, if left uncontrolled for even a few hours, it can migrate through the system, often with fatal results to the compressor on start-up.

Unlike most other mechanical equipment, refrigeration systems are vulnerable to attack from two common contaminants, air and water, which cannot be seen. Yet if either or both are present in a system, they quickly join in a common attack on the refrigerant and oil, and can cause corrosion, copper plating, acid formation, sludging, and other harmful reactions.

Absolute cleanliness is essential in a refrigeration system. In order to insure a reliable, trouble free unit, there are no compromises. Products such as "THAWZONE" or other alcohol based additives may create undesirable chemical reactions in a system. Additives of any type are not recommended and should not be used.

It is amazing to see the many foreign materials that have entered a refrigeration system and end up in the compressor. Filings, shavings, dirt, solder, flux, metal chips, bits of steel wool, mortar, sand from sand cloth, wires from cleaning brushes, lengths of copper tubing - all
have been encountered.

Of special concern for the safe proper maintenance of your on-board refrigeration system, is copper tubing. Copper tubing is made for many types of usage, but tubing intended for plumbing or water pipe may contain waxes or oils on the interior surface that can be extremely detrimental in a refrigeration system. Use only copper tubing especially cleaned and dehydrated for refrigeration usage. Soft copper tubing is available in rolls with the ends sealed.

Reasonable care during installation and service can keep contamination in a system at a safe and acceptable level:

1. Take care to keep tubing clean and dry.

2. Pass an inert gas through the tubing when brazing refrigerant tubes.

3. Take extreme care to keep foreign materials out of the system when it is opened for service.

4. Thoroughly evacuate the system at the time of original installation, or after exposure for long periods during maintenance.

5. Any time the system is opened, introduce a slight positive refrigerant pressure to prevent air from rushing into the open lines.

6. Install a new filter-drier in the liquid line each time the system is opened for service.

At Technicold we pride ourselves on using only the highest quality components to build marine cooling systems that we believe are the finest on the market. One example of this philosophy is the Tecumseh Hermetic Compressor.

The Tecumseh Hermetic Compressor is a direct-connected motor compressor assembly which is enclosed within a steel housing and designed to pump low pressure refrigerant gas to a higher pressure.

Because of the Tecumseh's housing type of shell, the housing interior is subjected only to suction pressure; it is kept protected from the discharge pressure created by the stroke of the piston. This point is emphasized in order to stress the hazard of introducing high pressure gas into the compressor shell at pressures above 150 PSIG.

In the illustration below, the major internal parts of a Tecumseh hermetic compressor are listed in the same sequence as that of the refrigerant gas flow through the compressor: