RSES Condenser Systems 4 — Questions and Answers
Question 1: On a hot day, an air-cooled condenser fan motor trips on thermal overload repeatedly. The most likely cause is:
- Low refrigerant charge
- High ambient temperature causing high amp draw (Correct answer)
- Clogged liquid line filter-drier
- Oversized metering device
Correct answer: High ambient temperature causing high amp draw
High ambient temperatures increase condensing pressure, which raises the load on condenser fans and can cause motor overloads to trip.
Question 2: What is the primary advantage of a microchannel condenser coil over a round-tube plate-fin coil?
- Easier field repair of leaks
- Higher refrigerant charge requirement
- Lower refrigerant charge and improved heat transfer efficiency (Correct answer)
- Better performance with hard water
Correct answer: Lower refrigerant charge and improved heat transfer efficiency
Microchannel coils use multiple small parallel channels that improve heat transfer efficiency and significantly reduce refrigerant charge compared to round-tube designs.
Question 3: A condenser pressure too low in cold ambient conditions can cause which operational problem?
- Compressor overheating
- Liquid floodback to the compressor due to low pressure differential (Correct answer)
- High discharge superheat
- Excessive subcooling only
Correct answer: Liquid floodback to the compressor due to low pressure differential
Very low condensing pressure reduces the pressure differential across the metering device, causing refrigerant to flood back as liquid to the compressor.
Question 4: When checking a water-cooled condenser with a refrigerant analyzer, where should refrigerant NOT be vented?
- Into the condenser water loop (Correct answer)
- Into a recovery cylinder
- Into EPA-approved recovery equipment
- Into a refrigerant reclaim tank
Correct answer: Into the condenser water loop
Venting refrigerant into the condenser water loop contaminates the water system and violates EPA Section 608 venting prohibitions.
Question 5: The term 'head pressure control' in variable-speed condenser fans refers to:
- Maintaining constant suction pressure
- Modulating fan speed to keep condensing pressure within a target range (Correct answer)
- Cycling fans to prevent freeze-up of the condenser coil
- Controlling water flow through a water-cooled condenser
Correct answer: Modulating fan speed to keep condensing pressure within a target range
Head pressure control via variable-speed fans modulates airflow to maintain the condensing pressure within an optimal range across varying ambient conditions.
Question 6: Which type of condenser achieves the lowest condensing temperature relative to ambient conditions?
- Air-cooled condenser
- Water-cooled with cooling tower
- Evaporative condenser (Correct answer)
- Remote air-cooled condenser
Correct answer: Evaporative condenser
Evaporative condensers approach the ambient wet-bulb temperature, which is always lower than the dry-bulb temperature, giving the lowest condensing temperature.
Question 7: Scale buildup inside water-cooled condenser tubes is best treated by:
- Increasing refrigerant charge
- Chemical descaling or mechanical brushing of the tubes (Correct answer)
- Raising condensing water temperature
- Installing a larger condenser fan
Correct answer: Chemical descaling or mechanical brushing of the tubes
Mineral scale on tube walls acts as insulation; chemical descaling or mechanical brushing restores tube cleanliness and heat transfer.
RSES Condenser Systems 4
On a hot day, an air-cooled condenser fan motor trips on thermal overload repeatedly.
The most likely cause is: