ACHR News Troubleshooting Questions & Answers
September 08 Questions & Answers:
1. What did you prove about the unit’s control transformer with your observation of the fan motor when you arrived?
Answer: We proved that the transformer was operable. Without it, the indoor fan motor wouldn’t be able to operate because there would be no control voltage to the Indoor Fan Relay coil.
2. Which of the components did you eliminate as possibilities when you checked the contactor coil circuit?
Answer: We eliminated the High-Pressure Switch, Low-Pressure Switch, and Overload wired in series with the contactor coil. We also proved that the contactor coil was not open with this test that showed voltage across an open switch. (The CR contacts)
3. Which component is the source of the no-run situation?
Answer: The failed component is the Control Relay. We proved this when we measured 24-volts applied to the coil of the relay, and also measured 240-volts across the N.O. CR contacts wired in series with the contactor coil, and also measured 0-volts across the N.C. contacts wired in series with the Crankcase Heater. If the Control relay was operable, the N.O. contacts would have been closed and the N.C. contacts would have been open. We proved that the contacts did not change position due to the voltage readings we noted.
November 08 Question & Answer:
1. Which component has failed?
Answer: The failed component is the blower motor. In our tests, we showed an infinity reading from the white wire (the common connection to the motor start and run windings), to all other colors that represented the individual motor windings for the various motor speeds. Since the motor was cool to the touch, either the internal overload protector is (and will forever remain) open, or there is a break at some point in the internal wiring to the common connection of the motor.
The flashing LED encountered upon arrival at the customer's home indicated either an open flame rollout switch or an open limit switch, and our ohmmeter tests and physical inspection indicated that the rollout switch was closed, and the limit switch was open. The root cause of the open limit switch was the failure of the blower motor, which caused an over-temperature situation...which caused the limit switch to open.
January 09 Question & Answer:
1. What design flaw is responsible for the specific air flow problem described?
Answer: The design flaw responsible for the air flow problem involving the branches closest to the plenum is that there is no trunk reducer. In our illustration, the plenum was shown as the same size for its entire length. The result is degraded air flow and the customer's complaint about the lack of comfort in the two rooms. A trunk reducer at the proper location (between the 5th and 6th branch ducts in the particular illustration that accompanied our problem description) will improve the air flow through the branch ducts located closest to the air handler.
March 09 Question & Answer:
1. Which component was replaced to get the furnace operating again?
Answer: The blower motor run capacitor was replaced. The wiring diagram showed the capacitor rating to be 5.0 MFD. Our meter test showed 2.5 MFD.
May 09 Questions & Answers:
1. What was the superheat reading supposed to be for this unit?
Answer: 15 Degrees.
2. What was the actual superheat of the unit?
Answer: 20 Degrees
3. What is your diagnosis?
Answer: The unit is undercharged. A higher-than-normal superheat indicates that the unit is low on refrigerant.
July 09 Question & Answer:
Which component has to be replaced to get this unit cooling again?
Answer: The component that needs replaced is the potential relay. We proved this when we got normal resistance readings on the compressor and potential relay coils, and also got normal microfarad readings on the capacitors. But we got a reading of infinity at the terminals of the switch contacts. On the potential relay the switch wired between terminals 1 and 2 are normally closed. And, since we disconnected the power and removed all wiring connections in order to test all components in their normal state, the reading should have been continuity, not infinity.
September 09 Question & Answer:
What is the next step you need to take to resolve the cooling problem with this equipment?
Answer: The Low-Ambient Control needs to be replaced. When the temperature drops, the control is supposed to break the circuit to the condenser fan, which maintain proper high-side operating pressure. In our problem situation, we found the condenser fan motor operating in a low-ambient condition and the switch not breaking the circuit.
November 09 Question & Answer:
What is the next step you need to take to resolve the problem with this equipment?
Answer: We need to change the wiring on the blower motor from low to medium-low speed. Our temperature rise test showed the temperature differential between the return and supply air to be 60-degrees, while the manufacturer's specifications were 55-degrees. By increasing the fan speed, the higher volume of air flow through the heat exchanger would result in the correct temperature rise, and also promote the necessary air flow to the problem bedroom.
January 10 Question & Answer:
What is the next step you need to take to resolve the problem with this equipment?
Answer: The next step is to replace the dual capacitor. Since there was no microfarad reading shown on our meter with a check between C and F, it indicated that the Fan section of the capacitor had failed, preventing the PSC-designed fan motor from operating due to no circuit through the start winding. Without the fan motor operating, the compressor would would only operate for a short time before heating up and kicking off on overload.
March 10 Question & Answer:
What is the source of the problem that is responsible for repeated compressor failures in this unit?
Answer: The root of the problem in this situation was incorrect piping of the suction line. Without a pump-down in place, the piping should have been accomplished as we are illustrating in the accompanying drawing. With the piping directly down to the compressor, refrigerant migration to the compressor crankcase occurred during system off cycles, causing oil foaming on start-up and eventual mechanical failure of the compressor. Our system was shown without a liquid line solenoid that would have been part of a pump-down system.
May 10 Question & Answer:
Based on our tests, what direction does our troubleshooting take in order to solve this problem and get the unit back on line?
Answer: In this case, the direction of our troubleshooting procedures would shift to the refrigeration system. As our meter tests showed on the control voltage side of the system, there was no voltage to the contactor coil. When we considered the safety controls, we found with our voltage tests that the high-pressure switch was closed, the compressor safety thermostat was closed, and that the low-pressure switch was open. Since our unit was sitting quietly and not attempting to start, the indication is that the low-pressure switch is open due to a loss of refrigerant. To complete the repair, we would locate the leak and repair it, install a new drier, evacuate the system, and recharge.
July 10 Question & Answer:
What is the source of the problem with this refrigeration system?
Answer: The liquid line drier is restricted. We found a temperature difference between our two test points that was beyond normal, indicating a restriction in the flow of refrigerant. In a liquid line, when there is a restriction, it causes the refrigerant to "meter" in the same way that the controlled restriction of a metering device at the inlet of an evaporator meters the flow of refrigerant, and ultimately causes the refrigerant to change in state from a liquid to a vapor, and absorb heat. With the drier is restricted, it is behaving...sort of...like a mini evaporator and the absorption of heat is taking place, causing the excessive pressure drop between our two test points.
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