Refrigerator Troubleshooting Diagram

This metering device is a very popular type. It is used in both refrigeration equipment, commercial and residential, and air-conditioning equipment, both residential and commercial. The small, copper tubing is sized by its I.D. (inside diameter). The liquid line from the condensing unit might be Vi-inch copper tubing. When it enters the evaporator section, the liquid line restricts down to a capillary tube with an I.D. of perhaps .065 of an inch. By restricting the refrigerant, pressure is raised on the high side of the system. The length of the tube is also relevant to the pressures. You can see that this system has a fixed metering device. If a large heat load is placed upon this type of unit, it takes a long time to remove the heat load. You can see that the thermostatic expansion valve is far superior in responding to changes in heat load. The capillary tube system works well in home units, both air conditioning and refrigeration. Figure 15-14 shows the typical capillary tube system. Care must be taken to protect the inside of the tube from becoming restricted. This is the reason for the fine mesh strainer at the entrance of the tube. All foreign particles should be trapped here and contained.

In Fig. 15-13 a typical, simplified, thermostatic expansion valve is shown. In the type of equipment being serviced, this type of metering device is most effective. By using a device such as this in a piece of equipment, the cost is elevated. The use of this valve requires a receiver to be used also. If it cost more to manufacture a unit such as this, why not use a different metering device? The advantage of this type of metering device is its ability to respond to variable load factors. Look at the diagram in Fig. 15-13 again. The sensing bulb is mounted to the suction line at the outlet of the evaporator coil. If the temperature is too high, the valve will open to allow more refrigerant to enter the coil. If the temperature being sensed should become low, the valve will throttle down the amount of refrigerant flowing into the coil. That is the greatest advantage to this type of metering device, it senses gain in heat load and can compensate for it. For example, at a wedding when people are sitting inactively, the heat buildup will be low. If the reception were in the same room, and people started dancing, the heat load would increase. The device used in a commercial type of refrigeration system where people are constantly opening and closing the appliance works very well keeping up with the demand.

The evaporator coil is the component in the system that absorbs heat from the conditioned space. It is similar in design to the air-cooled condensing coil. It is also finned to create more area to contact air flowing across it. The evaporator coil is designed for a specific purpose, to control humidity and temperature. Some coils are de­signed for high de-humidification, others are not. Earlier in the book, I mentioned that perfect conditions would be 72 degrees F., and a 50% R.H. for most human beings. A special design is required to accomplish this. If an evaporator is being used to keep vegetables and fruit from spoiling, a different type of coil is needed for the removal of heat and not the moisture contained in the product. This is only one example of many applications. Each evaporator is different and is designed to perform a specific task.

The refrigerant is pumped into the evaporator coil and pressure is dropped upon entering. The entrance is usually at the bottom of the coil. The refrigerant enters the coil as a liquid and begins absorbing heat. By the time the refrigerant reaches the top rows of the evaporator coil, it should have boiled and turned into a cool vapor. It is this cooled vapor that returns to the compressor to cool its windings and then it is recycled into a liquid to be circulated again.

Boiling temperatures of refrigerants at one (1) atm of pressure.

When discussing the air-cooled condensers, it was mentioned that the ambient air temperature would affect the efficiency of the unit. The higher the ambient reaches over the design temperature, the more inefficient the unit becomes. For this reason, water-cooled units have made their entrance. Of course the water-cooled condenser has many advantages along with its disadvantages. Some areas use water-cooled units in residences and light commercial units. I cover it here for your information.

Water is used as the heat transfer medium in place of air. Wa­ter flows through a heat exchanger where refrigerants contained in separate piping give up their heat to the water. Figure 15-5 shows how a few typical condensers are constructed. Now that you’ve seen the actual condenser and how it is made, you have to get water to make it operate.

In making a selection of whether to use air-cooled or water-cooled, the source of water should be studied very carefully. Water can be secured from a well, city, seawater, brackish, lake, pond, man-made pond. You can see there are many options; however, the content of the water is very important. The reason is that you don’t want a constant battle to keep the condenser clean from minerals or rust. A very rapid buildup on the inner surfaces that causes an inefficient heat exchange is costly to maintain. An air-cooled condenser might be advisable in such a case, or perhaps a water treatment system that would be cost effective. In many areas where an apartment complex or a condominium complex uses a community tower, the maintenance fee is not too high if chemical treatment administered through the water tower is done on a regular schedule to keep the individual condensers located in the individual apartments clean. The individual air conditioning units might range in tonnage from two to five tons. It might be necessary for you to be aware of how the water works.

In Fig. 15-6 a tube-in-tube type condenser is shown. It is very common in residential package units. The package can be rucked away neatly in a closet where it hooks up to a common water riser that is usually built into the wall. All the apartments located above and below use the same riser. Each apartment has a set of valves on the main riser in the event the unit must be removed; the water valves can be closed. What happens when a water valve doesn’t close completely? Never, never, never cut a pipe until you are sure the valve is holding. If it doesn’t, you might be emptying a community water tower all over some expensive carpeting in someone’s apartment, as well as that in apartments below. If a valve doesn’t hold, it will be necessary to find the shut-off valves for the entire riser. The drain valves somewhere below till then have to be found in order to drain the riser so that new valves can be installed. It is always good policy to try and get all the owners on that riser to agree to renew valves at the same time. You might want to turn the whole thing over to another service company.

In water-cooled condensers, some are sealed and some are built with bolted end plates that enable a technician to service it. The sealed condenser such as the tube-in-tube is cleaned with the aid of an acid circulating pump. Both inlet and outlet sides of the water circulating circuit of the condenser are opened. Fittings are placed on both sides to accommodate water hoses. One end of one hose is placed in the inlet fitting, and the other end of the same hose attaches to the discharge side of the acid circulating pump. Figure 15-7 shows a typical acid circulating pump. The pump is set into a five gallon plastic pail. The other hose is attached to the outiet side of the condenser and the other end of the hose is laid into the bottom of the pail. A gallon of sulfuric acid is placed into die pail and circulated through die condenser. The same acid can be used again, but the acidity should be tested often with litmus paper. If the acid level drops, more acid should be added. In using this cleaning procedure, make sure there is plenty of ventilation. You might need a small fan to remove fumes. This procedure is continued for about an hour. It helps eliminate mineral deposits that insulate the condenser and hinder heat transfer. High head pressure is one of the symptoms of a possible condenser problem. Figure 15-8 is another type of sealed condenser called coil-in-shell. It too is cleaned the same way the rube-in-tube is cleaned.

Figure 15-9 is a tube-in-shell condenser. This type unit is used in refrigeration and air conditioning equipment from small tonnages up to very large units. Cleaning this type is more difficult to do. This condenser is constructed with end plates that are designed to be removed for cleaning. A long rod is used, something similar to a ram­rod used in rifle cleaning. A wire brush is attached to the end of the rod. With the aid of an electric drill (usually a ³/4-hp slow speed drill is used) each tube of the water circuit is cleaned. After the brush is placed through the tube, it is flushed with water. By holding a light at one end and looking down the other (again as in cleaning a gun barrel), one can see mineral or other deposits. The same tube might have to be reamed and flushed with water several times before the deposits break loose.

A quick way to check the efficiency of the condenser is to touch the water outlet side and the refrigerant (liquid) outlet side of the condenser. The refrigerant should feel warm, not hot. The water outlet should also be warm to the touch. If the outlet water pipe is cold, either too much water is flowing through it or there is no heat transfer taking place. If the outlet pipe is very hot, there is a restriction in the water supply.

The condenser is a length of tubing with fins placed perpendicular to the tubing. Figure 15-2 shows a typical air-cooled condenser coil. This type of condensing coil is used in all size units from an average window unit to a commercial system having a three digit tonnage rating. The amount of refrigerant circulated per minute has a direct bearing on the tonnage rating of the system. The tonnage rating of the unit will determine the physical size of the coil in an air-cooled condensing unit. In Fig. 15-2 the affected heat transfer from the coil to the ambient air is shown. You can easily see that the ambient air temperature will determine the heat rejection efficiency of the condenser coil. Air conditioning systems are designed for the areas in which they are to operate. For instance, in a certain geographical area the unit might be designed to maintain a 72-degree F. temperature in a conditioned space, at an ambient temperature of 95 degrees. As the variable ambient changes, so does the temperature of the conditioned space. Not going into the engineering of it, air conditioning systems have a design factor. The perfect operating temperature of a condenser for example would be 105 degrees F. If the ambient temperature begins to drop, the system begins to lose efficiency. In Fig. 15-3 a condenser cross section is shown. The air flowing over the coil must be controlled if the unit is to operate efficiently during low ambient periods.

Fan cycling is controlled with the use of a reverse acting high-pressure control. The switch closes on rise of head pressure. The cycling switch might not be enough in those areas where a cold prevailing wind blows through the condenser coil.

In the prevailing wind situation, face dampers are placed on the condenser coil and piped to operate with head pressure. The dampers shown in Fig. 15-4 are used on many commercial applications. The dampers move in proportion to the head pressure. The only time the damper is in its full open position is when the compressor is operating at its design temperature.

This is not important to residential installation, but for the light commercial usage it is. Just think about a store owner with a freezer full of meat, with a walk-in freezer that is inoperable due to a low ambient. Even in light commercial air conditioning this could be important in places like a banquet hall. In those areas where cold weather is a rare occasion, a quick and temporary fix might be a piece of cardboard placed in front of the condenser coil to block the wind; a small hole might then be cut in the cardboard to allow a small amount of air to pass through the coil so it will not get too hot. On the other side of the coin, if things are too hot, the same problem can occur. In this case, there could be a defective condenser fan motor that is not available for one reason or another. The proper placement of a water hose and a fine spray directed at the condenser coil can save the day for someone. It is some of these simple things that make the good technician better. I’ve always instructed students that most of the service call should be done mentally, before picking up a tool. Talking to the owner and thinking carefully during the diagnosis will save time and a lot of your energy. Thinking over the job first will enable the right tools to be selected and brought to the job site. I have watched many technicians almost walk themselves to death, back and forth from the service truck to get the tools they forgot. Pre-planning or pre-thinking can help eliminate the condition. Refrigeration and air conditioning equipment must operate at their design temperature and pressure, in order to perform their specific job. Table 15-1 shows an example of some operating pressure found in general air conditioning, (high-temperature refrigeration). The equipment listed in the table are air-cooled condensers with a DX (direct expansion) evaporator. I want to say once again that when replacing a part, when it has a specific type of function, the part replacement should be exactly like the part being replaced. This is a very critical point when replacing a fan motor or fan blade. For instance, if a motor that drives the condenser fan blade is being re­placed, and the speed is less than the original, the unit might function alright on cooler days. When the ambient temperature rises, the fan will not turn fast enough to provide proper heat transfer. This will cause the unit to be less efficient on the hotter days of the year. Not only will it drive the owner crazy, it will drive the next service technician crazy trying to find the problem on the cooler day. There are certain relays and electrical parts that might be used in a replacement situation and still perform the same task as the original. Remember that in certain items within the unit, replacement parts must be the same. Another example would be replacement of a section of capillary tubing. If the exact I.D. (inside diameter) is not available, a different size and the exact length of the original won’t work. If the size is changed, so is the operating pressures which in turn affect the design factors of the unit.