HVAC Study

Delta T is calculated by using return air temperature minus supply air temperature, the value is called Delta T. For example, if the return air temperature is 75, and the supply air temperature is 65, then the Delta T is 75 - 65 = 10.  The normal range for delta T should be between 18 and 22. The higher Delta T normally means your fan is too slow, that is, air sits around the evaporator too long, lower Delta T normally means your fan is too fast, that is, air sits around the evaporator too short, had to no chance to condensate, so the fan needs to speed up a bit. Notice that Delta T gets affected by many factors, in some cases, Delta T of 15 is probably perfectly ok. but 20 may not be ok at all.

 if the capacitor marked 45/5 for example, then the Fan to common should be tested around 5 mfd, then the Herm to common should be tested around 45 mfd, there should be also +- like 6%, that will give a range. If they are out of the range, then the capacitor should be replaced. Also if capacitor is bad, when you manually push the contact, the condenser will try to start with some sound, but eventually it cannot, with this test, you can pretty much confirm that the system most likely need have capacitor replaced. in terms of the wiring, herm goes to condenser, fan goes to fan, common goes to L2. in terms of the color code, fan wire should be brown, common should be blue, herm should be yellow, but sometimes the color get messed up, you will have to make sure the wire (whatever the color might be) are connected to the right terminal. So to make it even more clear is that the herm terminal on capacitor should be connected to the compressor S(tart) terminal. C(ommon) on capacitor should be

DATS - Discharge Air Temperature Sensor.    This device is mounted on supply air duct, the DATS senses the delivered air temperature and cuts off the heating or cooling when the delivered air temperature goes above or below normal operating limits.  The sensor requires 2 wires to connect to the zone board. The two wires should be connected to the board's DATS connector. OT - Outdoor Temperature (sensor).    This device detects the ambient temperature, directing the zoning panel when to switch to the auxiliary heat source based on a low balance point setting. The two wires should be connected to the board's OT connector. LED lights   HZ432 Installation manual    

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.