Air conditioning parts specialist AP Air Europe Ltd has provided guidance for workshop operatives involved in vehicle AC servicing, regarding the interpretation of information from gauges and pressure readings on service stations.
“The pressure readings on your air conditioning service station can tell you a great deal about how the system is performing and help detect any major issues within it,” said Mike Beswick of AP Air Europe Ltd.
“The AC system is divided into two halves, the low pressure side and the high pressure side. Understanding the relations between the two pressures will help you understand what is happening within the AC system.
“Normal operating pressures on the high and low sides should remain within the following ranges (low side 20psi-50psi, high side 80psi-250psi) to ensure the best performance of the AC system. If either of the readings are outside of these ranges, it could mean that there are operating issues within the AC system that need to be looked into and resolved.”
Before undertaking a pressure test of the system, Mike said, the user must ensure that the system is in working condition.
“First you need to ensure that the system has the correct amount of refrigerant and at least 1.5- 2 bar /25 – 30 PSI pressure in the system to enable the compressor to run.
“The static pressures should be read before the vehicle is started. Both gauges should be close to equal pressure readings; if the pressure readings are too low, this indicates there is not enough refrigerant in the system, and investigations into a possible leak should be made.
“If the static pressures are as they should be you can now check the working pressures of the system. To do this, ideally you need to let the vehicle idle so that the engine reaches normal running temperature. Once the engine has reached its normal temperature, turn the AC on, set it to recycle and on full.”
The next step is to look at the gauges and watch the pressures as the compressor comes in and out.
Mike continued: “If the readings stay static, you know that the compressor is not pumping, which could be a compressor fault or an electrical fault in the system and you would then need to find the fault. Remember that your pressure readings will be affected by the ambient temperature; for example, on a hot day your readings may read higher than they would on a cold day.”
Mike highlighted various Issues that could cause the high side or low side to operate outside of the normal parameters.
“Too much or too little refrigerant will affect the working pressures of both sides of the system.
“Too much oil or dye in the system will affect the working pressures, as will some additives such as an AC booster/leak-stop,” he added.
“Blockages or any kind of flow restriction within the air con circuit, such as debris from the compressor or broken down receiver drier, moisture and contaminated refrigerant will all have an effect on the high and low pressure readings.
“A blocked condenser or blocked TXV valve would also have a detrimental effect on the pressure readings of the system. Leak-stop being incorrectly used in the system could cause a blockage.”
In addition, Mike explained, insufficient air-flow through the condenser would impact the readings – for example, if the condenser fan was not working, fins were missing from the condenser or the condenser was clogged with leaves and debris, reducing the air flow and the cooling capacity.
“A failing compressor would also see the pressure readings staying static, as there would be no compression of refrigerant to create high pressure and no suction on the low side gauge,” he concluded.