Informational Guide

What is Head Pressure in HVAC?

Reducing high head pressure can be a way to lower your HVAC energy costs. Read this complete guide on how to fix high HVAC head pressure.

by Josh M

HVAC machines use a lot of energy, especially during the hotter months when they are most active. When it comes to HVAC machines, head pressure can determine their efficiency. Reducing high head pressure can be a way to lower your HVAC energy costs. So we put this comprehensive guide together on how to fix high HVAC head pressure.

Head pressure, also called discharge pressure, is a type of pressure in pump systems determined by the height difference between a discharge point and some fluid. HVAC systems work by compressing vapor to cool things.

Sometimes, this vapor can build up near the top, creating very high pressure. Higher head pressure causes more energy as it takes more energy to maintain that pressure.

Normal head pressure for an air refrigerant HVAC system is approximately 58-80 psi, depending on the exact ambient indoor temperature.

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The Importance of HVAC Head Pressure Control

Head pressure is a necessary part of HVAC systems as they are part of the pumping mechanism that moves liquids through the system. However, when head pressure gets too high, the electric motors have to work harder to maintain that pressure.

The result is that a higher head pressure in the compressor pulls more electricity. This is one reason why high head pressure can cause cooling bills to skyrocket during the summer.

Conversely, low head pressure can cause insufficient cooling as not enough liquid is being moved through the pipes. So the goal is to find a pressure range that is neither too high nor too low.

Common Causes of High Head/Low Suction Pressure (+ What to Do)

  • Faulty condenser fan motor.
    A bad fan motor can also manifest as a rattling sound coming from the condenser. Sometimes the fan might just be loose, and other times it may need to be replaced if the frame or blades are cracked or broken.
  • Dirty condenser coils.
    Dirty condenser coils reduce their efficiency and prevent pressurized vapor from condensing. You can clean dirty condenser coils with a foaming condenser cleaner, but you should not clean them with just water and a cloth.
  • Blocked refrigeration device.
    A blocked refrigeration device can increase pressure by bottling up coolant liquid. Refrigeration devices like tubes can become blocked by solid materials or bent to restrict liquid flow.
  • Overcharged refrigerant.
    Overcharged refrigerants can be pushed into the suction line and get over the crankcase. This can cause compressor damage and compressor failure. This can be fixed by draining the system of refrigerant liquid.
  • Non-condensing gases in the system.
    Non-condensing gases can contribute to pressure as they do not phase change to a liquid. You can remove these gases by draining the coolant line.
  • Extreme operation over-designed specification.
    If your HVAC system is operating in extreme conditions, then it can create high head pressure. In these cases, you need to recalibrate your system so it is not taxed as highly.

Common Causes of Low Head/High Suction Pressure (+ What to Do)

Bad or leaky compressor valve.

High suction pressure is most likely a sign of a bad compressor valve. This can also result in lower head pressure than normal and sub-optimal cooling. Turn off the condenser fan unit and see if the pressure does not fall. If it does not, then the problem is likely condenser valves, and they need to be replaced.

Worn compressor piston ring.

A bad piston ring will manifest as leaky discharge gases resulting in low head pressure. Piston rings might be misaligned or may need to be replaced entirely. Worn compressor rings can be replaced by turning off the compressor array and disassembling it. Make sure you know the dimensions of the worn piston ring for replacements.

Leaky oil separator return line.

A leaky oil separator line can also cause low head pressure. Common signs of a leaky oil separator include a high crankcase volume, a loud whistle noise from the oil separator, or a foul smell. A leaky oil line needs to be replaced as soon as possible.

Refrigerant under-charge.

A system is a refrigerant undercharge when the amount of refrigerant in the system is lower than the factory-set level. Under-charge refrigerants will not build up enough condenser pressure to condense and so will not regulate temperatures as effectively. Conversely, a system with too much liquid refrigerant can have high head pressure.

People Also Ask (FAQ)

What is head pressure control?

Head pressure control refers to systems that regulate head pressure and keep it at optimal levels.

What are the symptoms of a bad expansion valve?

A bad expansion valve can manifest as blowing warm air or frost on the vents.

Is the discharge line high or low pressure?

Discharge lines should be high pressure, though not too high, or else you get high head pressure problems.

What is the suction and discharge pressure for r22?

Suction pressure for r22 is 68 psi and discharge pressure is usually at about 250 psi.

Why is my suction line warm?

If your suction line is warm, that could be a sign that the system is low on freon or there is a vacuum in the suction line.

Conclusion

Head pressure is an integral part of an HVAC system and needs to be at the right levels. Making sure that head pressure is at the right levels will make your HVAC system last longer and perform more efficiently.

Josh M

My name is Josh and I am obsessed with the HVAC industry. I created this website to help HVAC techs of all levels get the best out of their heating & cooling systems. I have spent thousands of hours studying air conditioners, heaters and home air products so you can learn & buy with confidence. Learn more about the team here.

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