Pressure switch

Pressure switch is the safety device that proves the ventor motor is working (motor above burners connected to vent). It has vacuum lines that are connected from the pressure switch to the ventor motor that measure a neg air pressure. All furnaces will have different pressures required to operate properly, most times the pressure will be written on the switch measured in inches water column.

Problems with pressure switches

  • Vacuum lines port plugged
    You will get open pressure switch error code, It can easily be fixed then you should reset the furnace to delete error code.
    Over time moisture will build up in the vacuum line port then dry up causing it the plug off. I have found the build up on the motor side of the vacuum line that was bad enough to shut down the furnace causing no heat. The vacuum line can be removed and the hole cleaned out with a small Alan key or anything small enough to fit in the hole with out breaking off. After cleaning it out you would need to shut power off at the furnace power switch to delete error code.
  • Pressure switch fails closed
    Normally this would indicate a failed pressure switch, The furnace will test to make sure the switch is open before starting the ventor motor. The contacts in the switch are either stuck together or moisture has entered the switched and seized it in the closed position. The switch will need to be replaced then you should make sure the vacuum lines are sloped back to furnace so water will not enter the switch again.
  • Pressure switch fail open
    First and most obvious would be failed ventor motor, check 110 volts to motor and if it has seized.
    The most common problem on high efficient furnaces would be frost or water in the vent. First off the furnace being high efficient will produce water due to low vent temperatures and condensation in the vent pipe. Motor ventor motor has been replace recently then make sure orfice plate after motor is in place
  • Water I do not like horizontal vent pipes on furnace but sometime they must be done. If the pipe sages a little and water collects it will block off the pipe, Very important to have the pipes properly supported. When the Vent pipe is repaired it should drain back to the furnace where the water will be routed to a floor drain.
  • Frost the exhaust on the furnace is warm and moist, sometime the intake which is very close to the exhaust will suck in this warm moist air and mix it with cold air producing frost. Frost will plug up the intake pipe causing the furnace to fail, the exhaust vent should be extended 8 inches past the intake. Also you should be careful of fences and other obstructions the exhaust could rebound back to the intake pipe.
  • Faulty switch

Anytime I am working on a furnace or during maintenance I will test the pressure switch for faulty contacts. I will start the furnace up and when the burners are on lightly tap the pressure switch if it stops the furnace then it should be replaced since contacts are not making a good connections internally.

  • How to test the pressure switch

Pressure switches are on the safety circuit of the furnace so that means it is 24 Volts a/c. Test from common to either side of switch when motor is running you should have 24 volts on each side. Once it is established you have power then you can connect meter similar to the way I have on the picture below. Connect Positive to one side and Negative to the other, when the ventor motor is running the meter will read 0 Volts. If you have 24 Volts, the pressure switch is open and not proving the ventor motor. Or you test any Voltage between 1 to 23 Volts then you have bad contacts and the full power is not getting through causing the furnace to fail. On a few furnaces I have found the ventor motor seams to be running fine and power is good but fails on pressure switch. When this happens it is best to record the Voltage from one side of the pressure switch to the other because the motor could drop rpm for very short time. The short drop in power is enough for circuit board to notice but not enough for you to notice.

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Flame Sensor failure video

In this flame sensor video you will see the sequence a furnace will take when you have a flame failure. The burners will try to light 5 times then go into lock out for 3 hours before it will try again. Another thing to keep eye on is the diagnostic light on the circuit board of the furnace located middle to the left side. You will see it flashing different codes count the flashes as it changes 4 times. short and long flashes

  • 1st code 12 meaning blower delay time, will change to next code solid light on after 34
  • 2nd code will be on solid for call for heat, flames fail and change to code 34 after 50 sec
  • 3rd code will be 34 for ignition proving failure, will change to code 14 after 4th try to ignite after 2 min 48 seconds
  • 4th code 14 ignition lockout. The furnace will be locked out for 3 hours before it tries again, you will need to reset power for furnace to try again by shutting power off then back on after a couple minutes or turning temperature down then up again.
    95 percent of the time the problem is only a maintenance issue and just needs the flame sensor cleanedClick on this link to see the video furnace flame failure video

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Thank you for visiting my blog I would appreciate any feedback I can get, Please leave a comment on whether my information has helped you. I am always interested in more topic to write so feel free to leave a comment asking about anything related to HVAC-R (Heating, Ventilation, air conditioning, refrigeration).

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Furnace filter

There are a few different types of furnace filters; they all have different capacities to clean the air and last different durations. On the side I have a link that will connect you to a chart for MERV (Minimum Efficiency Reporting Value) ratings and what each will clean out of the air. Every house is different for durations filters last depend on house (rugs, animals, etc) and area (construction, dusty areas, etc)

  • First one is flat; the surface area is only that of the filter. These filters will last 1 month 1 – 4 MERV
  • The next type of filter is the one I have pictured here, how is works is the media bends back and forth so if you were to stretch it out you would have material 3 times as long. This means they will last 3 months instead of the typical once a month filter changes. The filter would fit in same filter rack as regular filters and clean house better 4 – 8 MERV. Check out this filter on my affiliate website Amazon.
  • Another type of filter is the box type they can be 4 – 5 inch thick and require professional installation. Best part about this filter is that it only needs to be changed once a year, and are MERV 10 – 16. This is my recommended filter and is the same one I use in my house, It makes everything easier because you only have to change filter every fall not 1 or 3 month
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Thank you for visiting my blog I would appreciate any feedback I can get, Please leave a comment on whether my information has helped you. I am always interested in more topic to write so feel free to leave a comment asking about anything related to HVAC-R (Heating, Ventilation, air conditioning, refrigeration).

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Alarm for home

For holidays Especially in the winter time many people fly off to hot places to enjoy the warm weather not thinking about their house. One of the hardest part of the job I found was going to such a house when their furnace had broken down causing the house to get very cold breaking water lines and causing extension damage. I have seen houses where the furnace had stopped working due to minor problems, which could have been avoided if they had a low temperature alarm. Water lines would freeze then it warms up outside and the water lines break open spraying water all over house until they returned home.

Insurance company would not pay for damage because of a little clause they had for houses when they are unoccupied. Most insurance company’s clause say the house must be check every 72 house or insurance will not cover damage. I recommend talking to your insurance company about how often the house should be check when going on vacation. The grace time changes with each insurance company and each agreement.

One way freezing your house could be avoided is with this little thermostat, all you need to do is plug into a lamp and ask neighbor to watch for a light on. If they do see light they should call an emergency number you have setup with them. But of course light bulbs can burn out or electrics fail so be careful to still have someone check house as per insurance company requirements. Check out my affiliate Amazon for this alarm

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Furnace flame rollout safety

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This is a picture of a flame rollout safety switch it will trip at a set temperature. The temperature set point of the rollout is designed to open when the flame is coming out the front of the burners

  • Possible heat exchanger has a hole or big crack.
  • Another possible cause is a combustion air intake pipe getting a plugged screen, Which will cause the room to work in A negative air pressure. Then air will be pulled in through the exhaust vent pushing flames out of heat exchanger and tripping the switch.

Between the wires the switch has a resettable button, but the cause of the problem should be found before leaving furnace. Never jump safety switch as it could cause property damage.

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How to test flame sensor

<a href=”Lennox 28M97 Angled Flame Sensor For Mpga Cmpe Cmpb 20467102 ” title=”flame sensor amazon”>How to test flame sensor

In the picture you will see a 1/8 inch round rod in the flame, that is the flame sensor. You need a multi meter that measures micro amps which you will connect in series with the flame sensor. The sensor is usually located on left side but on some furnaces it may be on the right side.

How the flame sensor works is by a small AC electrical charge going through the sensor and it uses the flame to carry the electrical power to ground. Burner surface to flame sensor is 4:1 ratio thus causing the AC current to change to DC current. If no flame present, dirty flame sensor, bad flame characteristics similar to flame lifting off or carbonizing there will be low or no micro amp draw and the control board will shut the flames off. After 3 to 5 tries the control board will lock the furnace out for 3 hours, which can be reset by cycling power or thermostat.

All furnaces have different micro amp readings some good at .8 while others need 6 you will need to find out the right micro amp reading for your furnace. The flame sensor has a coating on it to make it last a long time and will get worn off by over cleaning, so it is best to only clean rod when it is needed. If flame sensor requires cleaning more often then once a year it should be replaced, or check for other problems like vent stack temperature, gas pressure, or primary air need to be adjusted.

How to clean flame sensor

  • First find the flame sensor.
    Most furnaces you will find a white wire located on the left side connecting the flame sensor to the circuit board.
    Watch the furnace ignite you will see spark or orange glow in front of one burner and the flame sensor should be on opposite side, but I have seen them on the next burner from the igniter.
  • Shut power off to the furnace while you are working, you will find a light switch high on wall or in the ceiling.
  • Most furnaces have 1/4 inch screw that holds the sensor in place; any multi screwdriver without the bit will be 1/4 inch. Remove the screw(s) and disconnect wire
  • Once removed you can clean the sensor with a scotch brite pad, if you do not have one then just use a clean rag for now. Do not use sand paper or wire brush, as it will remove the protective coating and scratch the rod causing it to fail more often. Some people like to clean every year but I advice not to, It is best to clean only when needed since the protective coating will be removed with over cleaning
  • Once the rod is cleaned reconnect the wire and screws making sure the rod sits in the flame. Some times the burner and any grounding surface will get dirty and need to be cleaned as well.

Click here to see my post “first check thermostat”
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Thank you for visiting my blog I would appreciate any feedback I can get, Please leave a comment on whether my information has helped you. I am always interested in more topic to write so feel free to leave a comment asking about anything related to HVAC-R (Heating, Ventilation, air conditioning, refrigeration).

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link in picture to amazon parts

pilot flame colour orange or soft blue

Best pilot flame will be one that makes little noise and has a sharp blue colour

  • Orange pilot flame is called a carbonizing flame, Means that it is running with low primary air
  • Low primary air is due to dirty pilot you will need shut gas off and remove pilot orifice and clean
  • Soft blue flame is caused by low gas pressure to the pilot, Which can be adjusted on the gas valve . If by adjusting pilot does not solve problem then gas valve is restricting gas too much and may need replacing.
  • Sharp blue flame that is too noisy will be opposite as soft blue flame the gas pressure is set too high, Pilot flame could lift off the pilot housing and go out .
  • Pilot flame should burn around the top 1/2 inch of the thermocouple in order to produce the proper dc voltage to hold the safety open for the gas valve to operate.check my links on side bar for thermocouple/thermopile charts where you will see a chart on how to test thermocouple/thermopiles

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Thank you for visiting my blog I would appreciate any feedback I can get, Please leave a comment on whether my information has helped you. I am always interested in more topic to write so feel free to leave a comment asking about anything related to HVAC-R(Heating, Ventilation ,air conditioning, refrigeration).

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