Ask Experts Questions for FREE Help !
Ask

    Heating & Cooling Maintenance, Repair & Troubleshooting FAQ from NortherHeat

    Asked Dec 5, 2006, 04:39 AM 57 Answers
    Check out these tips and explanations, below, from our Heating and Cooling Expert. Of course, you're also welcome to post questions to this board for more information: Just click the "Ask about Heating & Air Contidioning" button at the top of the page.

    Last edited by RickJ; Dec 8, 2006 at 08:29 AM.
    Search this Question
    Share |
    57 Answers
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #41

    Feb 1, 2007, 03:23 PM
    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.
    Helpful (1)
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #42

    Feb 2, 2007, 04:09 PM
    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.
    Attached Images
     
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #43

    Feb 2, 2007, 04:14 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #44

    Feb 2, 2007, 04:27 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #45

    Feb 4, 2007, 09:56 AM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #46

    Feb 11, 2007, 08:52 PM
    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
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #47

    Jun 14, 2007, 02:03 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #48

    Jun 14, 2007, 02:14 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #49

    Jun 14, 2007, 02:23 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #50

    Jun 14, 2007, 02:30 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #51

    Jun 14, 2007, 02:36 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #52

    Jun 14, 2007, 02:49 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #53

    Jun 14, 2007, 02:53 PM
    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.
    Helpful
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
    Ultra Member
     
    #54

    Jun 14, 2007, 03:10 PM
    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.
    Helpful
    jack_Brisco's Avatar
    jack_Brisco Posts: 1, Reputation: 1
    New Member
     
    #55

    Aug 12, 2007, 07:53 AM
    Comment on NorthernHeat's post
    Quote Originally Posted by NorthernHeat View Post
    Thermostat wire color codes explained.
    Please note. Not all installers use the proper color codes when they install or replace equipment. It may be necessary go go to the furnace or outdoor unit to verify what wires are for what purpose. Also be sure there are no splices in the wire that could change the wire colors between components.

    • R (red) or Rh (Red heat) 24 volts from equipment.
    • Rc (Red cooling) 24 volts from transformer in cooling equipment.
      Note: If only furnace has a transformer and cooling equipment does not jumper Rc and Rh.
    • W (White) sends 24 volts to furnace control to start the heating cycle.
    • W2 (no standardized wire color, usually whatever wire color is available) controls second stage heat.
      Note: W2 is most often used for heat pumps to control what is called emegency heat or Auxillary heat, and most often will use the white wire.
    • Y (yellow) often (blue) is used, controls cooling unit (outdoor condensing unit) also is used for heat pump heat.
    • Y2 (no standardized wire color, usually whatever wire color is available) controls second stage cooling.
    • G (Green) controls the fan "on" operation of the furnace/air handler. Also often is used to start the blower for many electric furnaces.
    • C (common) most often brown but can also be black or other color available to installer.
    • O (orange) Energizes heat pump reversing valve for cooling (Trane and most other brands).
    • B (Blue) Energizes heat pump reversing valve for heating (Rheem, Ruud and Weatherking).


    How to connect the wires to a new digital thermostat.


    If my answer helped, please click Rate this Answer! Below. Thanks!
    The color coding details helped me solved my problem
    Helpful
    wirechaser1's Avatar
    wirechaser1 Posts: 1, Reputation: 1
    New Member
     
    #56

    Dec 13, 2007, 04:46 AM
    Comment on NorthernHeat's post
    Quote Originally Posted by NorthernHeat View Post
    Blower turns on but there is no heat.

    Thermostats only control a fan relay, fan center or circuit board to turn on the blower motor.

    Although these relay's are necessary for cooling to work, they have nothing to do with the heating operation or outdoor cooling section of the equipment.

    Electric furnaces may or may not use this relay controlled by the fan switch of the thermostat.



    If my answer helped, please click Rate this Answer! Below. Thanks!
    I did not know this. Thanks!
    Helpful
    xdonwang's Avatar
    xdonwang Posts: 1, Reputation: 1
    New Member
     
    #57

    Feb 14, 2009, 07:56 PM
    Comment on NorthernHeat's post
    Quote Originally Posted by NorthernHeat View Post
    Sequence of operation.

    Natural draft furnace.
    24 vollts is always present to the thermostat R terminal.
    1. When the thermostat closes its switch to call for heat, 24 volts is sent out of the thermostat on the W terminal.
    2. This 24 volts goes back into the furnace, then typically through 1 or 2 safety devices to the gas valve.
    3. If the standing pilot is lit. The gas valve opens, and the gas to the burners is then ignited by the pilot light.
    4. The heat exchanger is heated untill a device tells the blower to come on, usually a fan and limit control. Also see camstat fan and limit control.
    5. When the thermostat is satisfied, the switch in the thermostat opens, the gas valve closes, stopping fuel and the fan continues to blow untill the fan and limit cools, turning off the blower.


    High efficiency operation.
    24 vollts is always present to the thermostat R terminal.
    1. Thermostat sends 24 volts through white wire to furnace.
    2. Furnace checks pressure switch, and safety switch's for proper positions (open/closed).
    3. Draft inducer blower motor, starts to run.
    4. If vent and vacuum hoses are clear the pressure switch, closes. (only a few pressure switch's open to prove venting)
    5. After inducer plower purges the heat exchanger, either a pilot lights, a hot surface ignitor (HSI), or a spark begins.
    6. If the furnace is an intermittant pilot model, once the pilot lights, current is sent through the flame by a flame sensor, if current is present through the flame the main gas valve opens and the burners ignite.
    7. If the furnace is direct ignition, The HSI or spark ignites the flame. A flame sensor passes current through the flame, if current is present the main gas valve stays open and heat exchanger begins to warm up.
    8. Most high efficiency furnaces then use an electronic timer on the circuit board to start the blower after the burners are proved.
    9. Thermostat opens when desired temperature is reached.
    10. The gas valve closes, burners extinguish, and the timer starts again to turn off the fan.





    If my answer helped, please click Rate this Answer! Below. Thanks!
    Very accurate Thank very much
    Helpful
    vinpadalino's Avatar
    vinpadalino Posts: 13, Reputation: 1
    New Member
     
    #58

    May 21, 2009, 03:36 PM

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

Not your question? Ask your question View similar questions

 

Question Tools Search this Question
Search this Question:

Advanced Search


Check out some similar questions!

Ceiling Fan Troubleshooting & Repair Frequently Asked Questions [ 13 Answers ]

Check out these tips and explanations from our Electrical Expert. Of course, you're also welcome to post questions to this board for more information: Just click the "Ask about Electrical & Lighting" button at the top of the page.

Heating & cooling [ 1 Answers ]

I have a bryant hvac unit the blower motor does not work but it makes a humming noise Then the noise stops but no blower motor this just statred after a power outage Thank you for any help

Heating and cooling [ 1 Answers ]

HI I would like to get help to see if I have wired my thermostat correctly

Heating and cooling [ 3 Answers ]

My furnace come on and then starts to blow out cold air


View more questions Search