Leak Detection & System Diagnosis Flashcards
7 cards from real EPA 609 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Leak Detection & System Diagnosis flashcards as text
On a properly charged R-134a MVAC system at idle with moderate ambient temperature, typical low-side gauge pressure should be approximately:
Answer: 25–45 psi
A properly functioning R-134a system typically shows 25–45 psi on the low (suction) side at idle, reflecting normal evaporator operating pressure.
Abnormally HIGH high-side pressure in an MVAC system most commonly indicates:
Answer: A blocked or inoperative condenser or cooling fan
When the condenser cannot reject heat efficiently due to blockage or fan failure, high-side pressure rises as the refrigerant cannot condense properly.
Abnormally LOW high-side pressure combined with abnormally LOW low-side pressure most likely indicates:
Answer: Insufficient refrigerant due to a system leak
Low pressure on both sides is the classic signature of an undercharged system, typically caused by refrigerant loss through a leak.
A compressor clutch that rapidly cycles on and off (short-cycles) at higher than normal frequency typically indicates:
Answer: A low refrigerant charge triggering the low-pressure cutout switch
When refrigerant charge is low, suction pressure drops quickly, causing the low-pressure cutout switch to cycle the compressor off repeatedly before pressure can stabilize.
A 'bubbling' or 'gurgling' sound heard from the liquid line sight glass (where equipped) indicates:
Answer: Bubbles of refrigerant vapor in the liquid line, suggesting low charge or a restriction
Bubbles in the sight glass indicate the liquid line contains refrigerant vapor, which means the charge is insufficient or there is a restriction reducing pressure upstream.
High low-side pressure combined with high high-side pressure in an MVAC system can indicate:
Answer: A leaking or worn compressor not building adequate pressure differential
When a compressor cannot pump refrigerant efficiently, pressures equalize at elevated levels — the low side stays high and the high side cannot reach normal peak pressure.
After repairing a refrigerant leak, the technician must:
Answer: Perform a vacuum pull-down to remove air and moisture before recharging
Evacuating the system to a deep vacuum removes air and moisture contamination introduced during the repair, preventing acid formation and ice blockages after recharging.