Bob and Tim are on the second day of an inspection of an apartment house building that has multiple split-system heat pumps. They have inspected all 60 outdoor units on the roof. They are now going to inspect the indoor units.
In this troubleshooting situation, the equipment you’re servicing is a 240-volt, single-phase split system in a small office, and the customer’s complaint is that the system is blowing warm air.
Bob and Tim have arrived at Tim’s first service call. Tim asked Bob, “What is this call all about?” Bob said, “This is a new customer that wants us to take over the maintenance work for this apartment house.”
Replacing a compressor is neither simple for a technician nor inexpensive for the customer. Before replacing a compressor, a technician needs to ensure that it is truly defective. Unfortunately, sometimes good compressors get replaced as a result of a misdiagnosed problem.
For this column I want to discuss a real life situation regarding poor cooling in a residence and reduced airflow coming from the registers in the house. The air conditioner is a three ton (36,000 btuh), HCFC-22, split type, air conditioner with the A-coil in the plenum of the furnace located in the basement.
Btu Buddy has met Bob for lunch to answer some questions that Bob had about yesterday’s service call. Bob asked, “Why did that motor have two contactors and so many wires going to it? It seemed very confusing. I am glad that I tagged those motor leads when I disconnected the motor. I never would have figured out how to reconnect the leads.”
When a refrigeration system fails, many times the cause can easily be diagnosed. However there are occasions when the cause cannot easily be determined - either the true cause is unclear or the technician is unsure of a problem. How do you work through these jobs? One method used by some techs is to “read and record.”
Bob got a call to go to a convention center where the air conditioning system was not working. It was a 75-ton unit with one compressor. The system was many years old, but had been functioning fine, until now. After checking out the unit, an ohm check showed 0 resistance to ground.
A variable frequency drive (VFD) fails to vary the discharge-air fan speed. A motor overheats and fails prematurely. While each troubleshooting problem in an HVAC system presents its own unique set of circumstances, HVAC professionals may recognize such problems as possible power quality issues.
Actually, frost on the suction line only indicates that at the location where the frost is present, the suction line piping is below the dew point temperature of the surrounding ambient air and at or below 32°F. That’s it. It is neither an indication of a properly operating system nor a system defect.
