HVAC Study

Heat pump system basically works in both winter and summer time because it converts condenser and evaporator role. In winter time, the indoor unit becomes condenser and outdoor unit becomes evaporator, in summer time, the indoor unit becomes evaporator and outdoor unit becomes condenser. The liquid line out of the compressor always contains liquid, the vapor line into the compressor always contains vapor. When liquid hit reversing valve, things change in winter and summer mode. See the chart below: The refrigerant lines that connect the indoor coil with the outdoor coil are the gas line (hot gas in winter and cold gas in summer) and liquid line. The liquid line is always the liquid line; the flow reverses from season to season.

The most common HVAC problems by a true hvac service technician: Bad compacitor Low refrigerant Clogged condensation drain line Bad control board Bad condenser fan motor Blower motor or compressor shorted to ground (breaker keeps tripping) Very dirty furnace filter (medium grade filter) Tripped AC breaker (could be shorted circuit, or bad compressor) There are six way tie at #9: Empty refrigerant (very big leak) Very dirty condenser coil (clean the condenser coil using water hose) Bad contactor Evaporator drain pan leaks Mouse damage Broken wires There are two way tie at 10th place: Locked up compressor Insufficient compressor Other issues: Furnace switch was turned off Disconnect fuses blown Evaporator clogged (no filter or very low grade filter or filter is not changed for long time or filter is not covering the entire duct) Restricted metering device (TXV or piston, TXV more common) Bad thermostat Furnace door switch is not working right. 95% of issues related to electrical componen

When measuring static pressure, the unit of measurement used is inches of water column, which is often shown as an abbreviation such as “in. wc ,” “in. wg” or “in. H2O.” One key to interpreting and diagnosing static pressure is to first understand how pressures change throughout an HVAC system. Static pressure is the amount of pressure a fan has to push and pull against to move air through a duct system. Static pressure is exerted equally on all sides of a duct system. This pressure is similar to that found by blowing up a balloon. When measuring static pressure, the unit of measurement used is inches of water column, which is often shown as an abbreviation such as “in. wc,” “in. wg” or “in. H 2 O.” Supply Plenum A plenum is an air-distribution box attached directly to the supply outlet of the HVAC equipment that heats or cools the air to make the house comfortable. The ductwork that distributes the heated or cooled air to individual rooms of the house connects to the plenum.

With 95 F outdoor temperature and 80 F indoor temperature you can expect a 125 F condensing temperature, (ambient plus 30). 95 F + 30 F = 125 F Convert temperature to pressure, R 22 at 125 F = 279 psi Indoor temperature (80 F) minus 40 F = 40 F evaporating temperature. Convert temperature to pressure, R 22 at 40 F = 70 psi. So, what this means is that the normal operating pressure depends on the indoor and outdoor temperature.