Tips On Servicing Head Pressure Controls

January 31, 2004
Properly installing and adjusting the head pressure controls, which are used on larger refrigeration systems with outdoor air-cooled condensers, is important to overall operation.

The liquid drain valve and condenser bypass regulators can be in a horizontal or vertical section of pipe. Normally there is an arrow stamped on the body to indicate the direction of flow. It is critical that the valve is installed in the correct direction of flow.

When installing the valve, take every precaution to prevent moisture, dirt, or solder beads from entering the valve. These valves may be soldered into the line without disassembling as long as the flame is directed away from the valve body and the body is wrapped with a wet cloth.

The condenser bypass regulator should be installed in a manner that avoids trapping condensed refrigerant at the valve. The adjustment stem of this valve should not be located below its center line.

There are several items to check before you adjust the liquid drain regulator and the condenser bypass regulator at start-up.

1. The system should have a full charge of refrigerant.

2. All the controls and components should be checked to verify that they are operating properly.

3. The system should have a full load on it.

Making Adjustments

It is best to adjust these regulators when the ambient is near the minimum outdoor temperature. They can be adjusted above that point, but usually not above 65 degrees F.

The adjustment of the liquid drain regulator requires installation of an accurate pressure gauge at the inlet side of the regulator. Most will have an access valve directly on the valve body. Before attempting any adjustment, loosen the valve seal nut. Turning the adjustment screw clockwise raises its setpoint; counterclockwise lowers its setpoint.

Once the valve is adjusted properly, the seal nut must be tightened to lock in the setpoint and prevent it from changing. The design setpoint may vary from system to system depending on the refrigerant used and the application. Contact the system's design engineer or manufacturer to obtain the regulator's proper setpoint.

To adjust the condenser bypass regulator, install an accurate pressure gauge on the outlet of the valve. Before attempting any adjustment, the valve seal nut must be loosened. Turning the adjustment screw clockwise raises its setpoint and counterclockwise lowers its setpoint.

Once the valve is adjusted properly, tighten the seal nut to lock in the setpoint and prevent it from changing.

This type of regulator should be adjusted on actual operating conditions. This may require adjusting the valve during low ambient conditions. The setting of this regulator should be at least 10 psig lower than the liquid drain regulator. Again, contact the system's design engineer or manufacturer to obtain the proper setpoint of this regulator.

Correcting Problems

As with any system component, both the liquid drain regulator and condenser bypass regulator can develop problems and require service. Pressure regulators can either fail to regulate, fail to open, or fail to close.

Before servicing either of these regulators, all other possible system problems should be identified and corrected. Sometimes a condenser bypass regulator is blamed for system hunting. Before you attempt to adjust or service this regulator, check the thermostatic expansion valves (TXVs) to verify that they are functioning properly.

Contaminants within a pressure regulator can cause it to fail to open, close, or regulate. If you suspect contaminants are the cause of the problem, most regulators can be disassembled in the field without unsoldering the valve's body. Normally the core of the regulator can be unbolted from the body; the inner components of the regulator can then be cleaned and reassembled.

Some pressure regulators also incorporate a stem to manually open the regulator. This can be helpful when servicing a system. However, it can also be the cause of a system problem. If the regulator is manually left open, it cannot regulate the system. Be careful to verify that the regulator is not left set to the manually open position before you leave the job.

Joe Marchese is owner of Coldtronics, Pittsburgh. He can be reached at 412-734-4433,, or

Publication date: 02/02/2004