Simply put, a plenum is the ductwork/metal box, that moves air out of the furnace into the ductwork. For an upflow furnace the plenum sits directly above the furnace or cooling (evaporator) coil. For a downflow furnace the plenum is frequenty in the slab, under the furnace.

Here is a picture of a purge and balance valve, note the small screw (butterfly valve) is inline with the pipe, (open position) some of the older purge and balances have a small knob/lever. Turn it 90 degrees (closed) hook up a garden hose and open the boiler valve knob. Now if the pressure reducing valve is working it will let water into the system as you bleed the air out, when you are done and no more bubbles are coming from the garden hose close the boiler valve, open the butterfly again and be sure water pressure is back to about 12 psi.

Most boilers have a temperature and pressure gauge on top, inside or on the side of the boiler, if yous doesn't have a gauge it should. A domestic hot water boiler (not to be confused with a low pressure steam boiler) should run a pressure of about 12 psi cold and 18 psi hot. Note: Boilers have a pressure releif valve for safety, at 30 psi this valve will open and let water out of the boiler, and probably on your floor.

When you hear water running through your radiators it is almost always a sign that you have air in the system. See article for bleeding system.

Should I put the fan switch on "ON" or "AUTO"

There are several benefits to continuously running the blower. By continuously running the fan, you can even out the temperature in all the rooms of your home. In conjunction with an air cleaner, you can improve the air quality and reduce dust. Most experts say running the fan constantly does not reduce the life of the motor.

Then the nagative side of the issues are. Blower motor can consume 1 dollar a day or more to operate. Flexible ducts, in attics are poorly insulated, moving air continuously is inefficient and I've known it to cause ice damming in some newly built homes. Filtration becomes more critical. Poor filtration, grit and dust will build up faster in the furnace, filter, blower motor, blower wheel, and evaporator coil. Dust in motor bearings cause most premature motor failures.

Turn the knob on the gas valve to "pilot" and just wait for 5 minutes. Locate a 1/4" aluminum tube that comes out of the gas valve and follow it down towards the burner. There should be a shrouded device at the end of that tube, also a small copper wire going into it this device 'this is the pilot. Get an extension lighter and turn it on near the shrouded device. Now push the pilot valve down, it should light, now hold this button down for 1 minute. Release the button and the pilot should stay lit. If it doesn't you have a very dirty pilot, a bad thermocouple or gas valve. If the pilot stayed on, you are ready to light the furnace. Be sure the thermostat is "off", turn the gas valve to "on" now you are ready to turn the thermostat back to on.

Good luck

A typical condensing unit, (condenser) comprises of 4 major parts. The compressor (a pump) a fan, (to cool the refrigerant), a capacitor (simply put, aids the starting of the compressor and fan) and a contactor (uses low voltage to close the high voltage switch to the fan and compressor)

The compressor builds up pressure on the refrigerant, after the refrigerant is cooled by the fan, is converted from a high pressure/high temperature gas to a high pressure/low temperature liquid.

The evaporator. Is the cooling component of an air conditioner. High pressure/low temperature refrigerant is pushed through a metering device. Once inside the lower pressure evaporator coil, the refrigerant tries to evaporate. Remember evaporation is a cooling process, put some water on you hand and blow on it, it is cool. This is due to the molecules absorbing energy and moving away from each other. When warm indoor air blows across the coil the refrigerant absorbs the heat and cools the air.

The compressor is nothing more than a pump. It compresses the refrigerant, due to a metering device in the evaporator, the pressure of the gas increases. Remember using a hand pump to pump up you bicycle tires? The pump and hose got warm, even the tire although not that noticeably. The hot high pressure gas is condensed into a liquid by the condenser coil, thus releasing the heat outside which the refrigerant gained inside.

A typical air conditioner is designed for a 15-18 degree F split, that is, the return air temperature minus the supply air temperature. If the split is greater that 18 degrees F you probably have low air flow issues (same as reasons furnaces overheat). If the split is less than 15 degrees F your blower speed may be incorrect or you could be low on refrigerant.

Yes, am ais conditioner uses the blower fan in the furnace to circulate the cold air throughout the house. Some air conditioners are hooked up to an air handler, very similar to a furnace, but either has no heat, electric heat banks, or it could be a heat pump.

Yes, an air conditioner uses the fan and usually the low voltage controls of the furnace/air handler to move warm air through the evaporator/cooling coil of your air conditioner.

Temperature split should be about 15-18 degrees F, same as an air conditioner split, dependent on how cold it is outside. Supply air temperature minus the return air temperature should be about 15-18 degrees.

Manufacturers have used many different means over the years to defrost heat pumps. It could be based on run time, demand or both. In short, when the heat pump needs to get rid of the frost and ice build up on the condenser coil, it stops the fan, the compressor continues to run and the reversing valve changes the refrigerant direction. During this time, the coil in the outside unit gets hot and melts the frost. Steam is often produced during this defrost cycle.

The color coding details helped me solved my problem

I did not know this. Thanks!

Very accurate Thank very much

That is good to know, and a good refresher course!