A/C System Pressures, Troubleshooting

A/C Refrigerant System (R-134a) Pressures, Troubleshooting
- Check A/C refrigerant system pressures. A/C System Pressures, Checking

If system pressures are not correct,
- Refer to conditions/service solutions below.

A - High pressure remains at base pressure (engine OFF) or only increases slightly; low pressure drops quickly to suction pressure or lower or high pressure normal; low pressure corresponds to chart value: proper cooling performance is not obtained

- Low refrigerant charge
- Check for leaks with halogen leak detector Hitec H1400A-TEL or equivalent, repair/eliminate as necessary, evacuate and recharge system.


NOTE: If no leaks are detected, discharge A/C system and flush with compressed air and nitrogen, then evacuate and recharge system.


B - High pressure increases only slightly over base pressure (engine OFF); low pressure drops only slightly

- A/C compressor faulty
- Discharge A/C system.
- Flush system with compressed air and nitrogen.
- Replace A/C compressor, evacuate and recharge system.

C - High pressure above specified value; low pressure drops to suction pressure or lower

- A/C system line/hose kinked or plugged
- Feel A/C system lines/hoses (high and low side) for temperature drop (restriction).
- Inspect all lines/hoses for kinks or damage, replace as necessary.
- If obstruction is present, flush system with compressed air and nitrogen, then evacuate and recharge system.

D - High and low pressure normal; after A/C operates for a time, high pressure increases above specified value and low pressure drops to suction pressure or lower

- Moisture in system, restrictor icing up
- Discharge A/C system.
- Flush system with compressed air and nitrogen.
- Replace accumulator and restrictor, then evacuate and recharge A/C system.

E - Low (suction) pressure too low; low pressure switch -F73- switches A/C compressor OFF, proper cooling performance is obtained

- Check switching pressures of A/C refrigerant low pressure switch -F73-.
- Replace switch if faulty.

If switching pressures OK,
- A/C compressor faulty
- Discharge A/C system.
- Flush system with compressed air and nitrogen.
- Replace A/C compressor then evacuate and recharge A/C system.

F - Low (suction) pressure too low; low pressure switch -F73- switches A/C compressor OFF, proper cooling performance is not obtained

- Low refrigerant charge
- Check for leaks with halogen leak detector Hitec H1400A-TEL or equivalent, repair/eliminate as necessary, evacuate and recharge system
- Check switching pressures of A/C refrigerant low pressure switch -F73-.
- Replace switch if faulty.

G - Low (suction) pressure too high; high pressure normal or increases above specified value

- System is overcharged
- Using refrigerant recovery/recycling/recharging unit Kent-Moore ACR4, or equivalent, remove approx. 200 grams (7.1 oz) of refrigerant from system (remove several times if necessary).
- Repeat system pressure test.

If both high and low pressures are now normal,
- Discharge A/C system, then evacuate and recharge.

If high and low pressures still are not correct,
- Compressor faulty, replace.

H - Low (suction) pressure normal; high pressure normal, proper cooling performance is not obtained

- Too much refrigerant oil in system
- Discharge A/C system
- Flush system with compressed air and nitrogen, then evacuate and recharge A/C system.


NOTE: High pressure and low pressure service connections used on R-134a systems are a different size.