In order for an A/C system to work properly, it must produce the correct pressures on both the high side and the low side. Any obstruction inside the A/C system can create excessive pressures on the high side and extremely low pressures on the low side. When the pressures are not within specification, the A/C system will not cool efficiently if at all. Blockages can be detected by connected gauges to both the high and the low sides of the A/C system. Normally, blockages are found in the condenser and the expansion device.