Refrigerator Troubleshooting Diagram

Archive for the ‘Thermostats’ tag

Room Air Conditioners Thermostats

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The thermostat (or temperature control) stops and starts the compressor in response to room temperature requirements. Each thermostat has a charged power element containing either a volatile liquid or an active vapor charge. The temperature-sensitive part of this element (thermostat feeler bulb) is located in the return air stream. As the return air temperature rises, the pressure of the liquid or vapor inside the bulb increases, which closes the electrical contacts and starts the compressor. As the return air temperature drops, the reduced temperature of the feeler bulb causes the contacts to open and stops the compressor.

The advent of transistors and the semiconductor chips or integrated circuits has produced a more accurate method of monitoring and adjusting temperatures within a system. The microprocessor makes use of the semiconductor and chip’s abilities to compare temperatures and to program on and off cycles, as well as monitor the duration of each cycle. This leads to more accurate temperature control.

Figure 5-25 shows a microprocessor-based thermostat. As you can see from the front of the control panel, you can adjust the program to do many things and, in the process, save energy, whether it is operating the furnace for heat or the air-conditioning unit for cooling. These units usually come with a battery so that the memory can retain whatever is programmed into it. The battery is also a backup for the clock so that the program is retained even if the line power is interrupted.

Written by sam

February 8th, 2011 at 3:20 am

Posted in Room Air Conditioners

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Freezer Thermostats

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Freezers and refrigerators have the same theory of operation. The start relay for the compressor operates the same way as the start relay for a refrigerator. However, the thermostats are somewhat different.

On upright freezers the thermostat is mounted in the upper right-hand corner of the storage compartment in all manual defrost models. The thermostat knob in the manual defrost models is numbered 1 through 6 or coldest and off.

On all other models, remove the right-hand side cold ban trim and filler insulation. Loosen and remove the thermostat thermal element clamp from beneath the refrigerated shelf. Straighten the thermal element and attach a 3-ft length of cord to the end of the thermal element. Use tape. Remove the light shield and thermostat knob. Disconnect the wire leads and remove the thermostat from the mounting bracket. Pull the thermal element out of the insulation.

On the chest models the thermostat is located on the left end of the cabinet near the top of the unit compartment. The dial is marked off, normal, and cold. To stop the compressor during a normal running cycle, pull the service cord from the electrical outlet or turn the thermostat to the off position.

To replace the thermostat, first disconnect the power cord from the electrical outlet, and then remove the knob. Remove the thermostat mounting screws. Pull the thermostat into view in the machine-compartment opening.
Disconnect the wire leads from the thermostat terminals.

Remove the mastic sealer from around the thermal element where it enters the thermal-well trough in the cabinet outer wrapper in the machine compartment.

Before removing the thermal element from the thermal well, wrap a small piece of tape around the thermal element next to the opening of the thermal well.

Remove the thermostat from the machine compartment. Wrap a piece of tape on the new thermostat thermal element at the same location as the tape on the inoperative thermostat. Push the thermal element into the thermal well. To insure the correct length of thermal element in the well for positive contact, the tape on the thermostat thermal element should be at the entrance of the well. Replace the mastic sealer. Connect the wire leads. Install the thermostat mounting screws and knob.

Figures 13-13, 13-14, and 13-15 show three types of thermostats. The thermostats are set at the factory in accordance with the manufacturer’s specifications for cut-in and cutout. No adjustment should be made unless it is absolutely proven that the thermostats are not in accordance with specifications.

If a higher or lower range than is obtainable by the selector knob is desired, adjust the range (altitude)-adjustment screw.

On GE thermostats, the range-adjustment screw is reached through the small hole in the face of the thermostat. See Fig. 13-13. Turn the screw to the left to lower the cutout and cut-in. Turn the screw to the right to raise the cutout and cut-in temperatures. Turning the range screw to the right makes altitude adjustments.

The range-adjustment screw on the Ranco thermostats is located behind a removable cover. See Fig. 13-13. Turn the screw to the left to lower the cutout and cut-in temperatures, and to the right to raise cutout and cut-in temperatures. Turning the range screw to the right makes altitude adjustments.

Cutler-Hammer thermostats have cut-in and cutout temperature adjustment screws. See Fig. 13-15. Turn the screws to the left to raise the cutout and cut-in temperatures and to the right to lower the cut-in and cutout temperatures.

Both cutout and cut-in screws must be adjusted counterclockwise to compensate for altitudes above 1000 ft.

Written by sam

February 7th, 2011 at 2:15 am

Posted in Freezers

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