TROUBLESHOOTING
BLOCKAGES IN A/C SYSTEM CIRCUIT
A very useful diagnostic aid is the “Feel Test”. As the test implies it is a matter of quite simply feeling tubes and components for temperature drops, indicating possible blockage location.
By this stage you would be aware of what side of the A/C system should be hot and what side should be cold. But what also happens with the pressure gauge reading, sometimes they don’t make sense.
The location of the charging ports in relation to the A/C system MUST be taken into consideration. A pressure gauge reading could be high or low depanding on what side of the charge port the blockage is located. Use the “Feel Test” as well as the pressure gauges readings.
NORMAL SYSTEM
HIGH SIDE – Hot
LOW SIDE – Cold
BLOCKAGE HIGH SIDE AFTER CHARGE PORT
HIGH SIDE PRESSURE: High
LOW SIDE PRESSURE: Low to normal
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– High pressure switch will not deactivate the A/C system, low pressure switch might;
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– Compressor noisy;
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– High Side hose very hot before blockage;
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– High side hose very cool to warm after blockage
HIGH SIDE BEFORE CHARGE PORT
BLOCKAGE HIGH SIDE PRESSURE: Low
LOW SIDE PRESSURE: Low to normal
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– High pressure switch will not deactivate the A/C system, low pressure switch might;
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– Compressor noisy;
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– High Side hose very hot before blockage;
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– High side hose very cool to warm after blockage.
BLOCKAGE LOW SIDE AFTER CHARGE PORT
HIGH SIDE PRESSURE: Low
LOW SIDE PRESSURE: High
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– Low pressure switch will deactivate the A/C system;
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– Frosting of the low side hose/fittings before the blockage.
BLOCKAGE LOW SIDE BEFORE CHARGE PORT
HIGH SIDE PRESSURE: Low
LOW SIDE PRESSURE: Low to vacuum
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– Low pressure switch will deactivate the A/C system;
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– Frosting of the low side hose/fittings before the blockage.
ORIFICE TUBE
HIGH SIDE PRESSURE: Low
LOW SIDE PRESSURE: Low to vacuum
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– Low pressure switch will deactivate the A/C system;
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– Frosting of the tube after the orifice tube.
RECEIVER/DRIER
HIGH SIDE PRESSURE: High
LOW SIDE PRESSURE: Low to vacuum
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– Low pressure switch will deactivate the A/C system;
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– If the blockage is in the receiver drier itself, the outlet tube will be frosted
CHECKING REFRIGERANT CHARGE
Run the A/C system, place one hand at the outlet side of the orifice tube and one hand on top of the accumulator.
If the temperature of the accumulator is higher than the temperature after the orifice tube, then the refrigerant charge is not to specification. Add 150g and recheck.
CONDENSER BLOCKAGE
A change of state, where high pressure vapor forms into a high pressure liquid during the movement through the condenser, takes place within approximately the first 1/3 of the condenser. With this change of state a slight (depending on ambient temperature change takes place.
Using your finger, follow the tube(s) of the condenser (avoid burning your skin), you can feel where the change of state takes place. This change will however be quite subtle. But if you feel the difference in temperature before approximately the first 1/3, a blockage maybe present.
With the parallel flow design condenser, refrigerant flows through more than one tube so the possibility exists that the condenser will operate sufficiently in lower ambient. But when the ambience increases and greater refrigerant flow is required, a blockage in one tube will cause problems such as poor performance and excessive discharge pressures.