Undersized unit.

[marc5180]

As the title says, how what you check for an undersized unit?
Apart from the obvious like room not getting down/up to temp.

Things such as discharge/suction pressures, line temps Sh and SC.

[coolstuf]

Also high head pressure,high suction pressure

[nike123]

As the title says, how what you check for an undersized unit?

By calculating real heat load.

Apart from the obvious like room not getting down/up to temp.

Things such as discharge/suction pressures, line temps Sh and SC.

These are consequence of current room conditions, which may not represent actual needed capacity.
For example: after long period of standby, room envelope (walls, floors, ceilings) could accumulate lot of heat, and room cannot be cooled satisfactory for prolonged period, but after walls are at normal room temperature, capacity could be more than enough.

[Gary]

Assuming the system is functioning properly and has run for a prolonged period (cycled at setpoint for several days), you can plot a chart of percentage of run time versus a variety of outdoor conditions. You can then extropolate the point where outdoor conditions will result in 100% run time.

[Gary]

Technically, it is more economical to run a smaller system that can't quite keep up on the hottest day of the year, but the customer isn't going to like it. A larger system that can handle the hottest days will make him smile, even though it costs more to run on milder days than the smaller system would.