Suppose you are testing a Copeland 3D (Discus) compressor and your ohmmeter registers OL from line to line on all of the 3-phase legs. The compressor is cold so you determine that the compressor is not off due to an overheat/internal thermostat trip. Your early assessment is that the compressor is bad and must be replaced. You call your supervisor who immediately sees a red flag when you say all 3 windings are open. It may be a defective “inherent protector”. This happened to a service tech that I supervised a few years ago. And it did have a bad protector. Please see the following photo and wiring diagram for more information on how this all works and the numbers needed to obtain a replacement inherent protector. By the way, this part is located beneath the terminal plate and is mounted just above the motor windings in order to detect the first possible overheat situation.
One of the ways to assure that a customer’s case is performing as it should is to test the airflow. One of the best ways to do this is with a test instrument that measures feet per minute as illustrated.
Be sure to measure the airflow at the case discharge air outlet as illustrated below:
The manufacturer recommends that the best time to measure the case airflow is during the warmest time during defrost as the case cycle is terminating.
Below is a manufacturers chart detailing an example of a case specifications including the case design average air flow. Without the proper air flow, the case temperature will not reach the desired set point and the product integrity will suffer.
Members and guests got to check a fractional hp compressor for good/bad windings at the June 2017 Regular Monthly Meeting at the Middle TN Chapter. Jayson Goff, CMS was the seminar leader and had just returned from a winning battle over Stage 4 cancer. By the way, the compressor was deemed terminally ill by Larry Lynn, CMS and Doug Drake, CM, due to bad terminals. 😀
Routine maintenance of blower sheaves should include a close examination of the alignment of the motor and blower sheaves. Proper belt tension is also important to maintain the life of the sheaves. Groove gauges are often provided by belt and sheave suppliers to test the sheave walls for wear to determine the need for replacement.
Another important item to check is the RPM’s of the blower to determine if it is within the range that was established during commissioning by test and balance personnel or startup technicians. Once the sheaves get a measurable amount of wear, it becomes increasingly difficult to provide the proper air delivery of the blower due to lost RPM’s.
Rigid connections at the compressor are prone to crack or break from vibration and stress. The cause may be discharge gas pulsation or compressor movement because of high torque.
There is a simple way to prevent line breakage from these causes. Install vibration eliminators in both the suction and discharge lines. They should be the same size as the lines. Install the vibration eliminators parallel with the drive shaft on the compressor. It should only be clamped on one end.
A typical vibration eliminator has rigid copper ends to connect to the compressor and the system. Between the ends is a length of flexible tubing. It is covered with woven brass or stainless steel mesh for strength.
Relays are electrically operated control switches, and may be classified as either power relays or control relays, according to their use. Power relays are frequently called contactors. Control relays are usually known simply as relays.
As you can see in this illustration, there are four basic parts to the relay. The coil of wire becomes magnetized when a voltage or current is applied to it. The armature is connected to the contacts. (Generally, the armature and the contacts are electrically isolated from one another.) The spring keeps the relay in its normally open or normally closed position when no power is applied.
There is a lot going on in the world of Refrigeration. Electronics, alternative refrigerants and new ways to service equipment. One way to keep ahead of these changes and grow your business is to sign up for Refrigeration Contractor Weekly.
Special considerations must be taken when installing condensers in cooler climates. During the colder weather, a winterizing valve should be utilized to maintain head pressure. This valve is actuated by a pressure difference between its inlet and outlet. The figure shows a “Winterstat” brand. Other valves may be used such as a “Headmaster” valve. If system pump-down is a desired feature, the receiver must hold the normal refrigerant charge plus the condenser charge with the bypass valve operating ̶ that is, partially open or intermittently opening and closing.EXCERPT FROM “TOOLS, CONTROLS AND TROUBLESHOOTING“, available from the ONLINE STORE at RSES.ORG.
Troubleshooting and servicing refrigeration and air conditioning systems can be a challenging process for both the entry level and experienced HVACR technician.
Regardless of your experience, size of the equipment, or location, to troubleshoot the system it is essential that you have a solid understanding of the fundamentals of refrigeration – including the principles of superheat and subcooling. READ MORE HERE