"HVAC - R22-Based - What Are Normal Pressures (Temperatures)?"

 By Ron Stultz

16 September 2012

Updated: 20 July 2017

Summary: it is Environmental Protection Agency (EPA) illegal to mix coolant types in a heating, ventilation and air conditioning (HVAC) system. In my (2) R22-based HVAC systems, the low pressure side is 40 and 45 degrees Fahrenheit (F) while the high side is 110 and 115 degrees.

Background:

Have (3) HVAC systems: (2 ton Goodman heat pump); (5 ton York) and (2 ton York).

All systems use R22 refrigerant.

A HVAC gauges manifold shows and temperature for both low and high pressure lines as seen at the compressor.

The low pressure side is the larger of the 2 pipes coming out of or going into the outside compressor unit.

The high pressure side is the small diameter line.

The low pressure side carries R22 gas while the high pressure line carries R22 in a liquid state.

R22 changes from a liquid to a gas in the evaporator coils of the air handler.

Normal temperatures:

With compressor running and as reference, on a 90 degree F. day:

- Goodman runs 45degrees F on low pressure side and 115degrees F on high pressure side.

- 2 ton York runs 40degrees F on low pressure side and 110degrees F on high pressure side.

If temperature of low side is at or close to 32 degrees F, your system is probably experiencing freezing evaporator coils.

When evaporator coils freeze over, you get limited or no air of your system.

Rule of thumb:

5 ton York had evaporator coils (in attic air handler) replaced with non-York coils and thus "miss-matched" system.

For this system, the rule-of-thumb for temperatures is used.

Rule-of-thumb? Determine outside ambient temperature and high side temperature should be 20 to 30 degrees about ambient. So in my case, my 5 ton miss-matched system runs 40degrees F on the low pressure side and 120degrees F on the high pressure side on a 90 degree F day.

Adding refrigerant:

If you add refrigerant, you add it to the low pressure line as a gas.

Increasing the pressure and thus temperature of the low pressure side of the compressor will also raise the pressure and thus temperature of the high pressure line.

The target for adding cooling is the high pressure temperature of approximately 110 degrees F.

Never measure or try to add coolant if the evaporator coils are frozen over.