If you a hear a beep coming from your furnace, most likely it’s indicating that you’ve got trouble with your ventilation system. On the Deluxe Blend Air II systems, you can silence the beep by sliding the lever marked ‘alarm’ to OFF. Remember that when you start troubleshooting the system, this lever will need to be turned back on. The ventilation system not working is not considered an emergency and can be left off for a few days if necessary. Leaving it off for a short period of time will have no effect on your furnace. Leaving it off for a long period of time may cause condensation to build-up in your attic and affect the air quality of your home.
Because a typical mobile home is built fairly tight (I know — your heating bill may say otherwise), a ventilation system has been added to bring outside air into your home. In the Deluxe model, the same system also removes moisture from your attic. The control box for this Blend Air system is generally located in your furnace compartment or on the furnace itself.
Part of the ventilation system is a pressure balancing damper. This is the vent you may have found on an exterior wall and sealed it shut because you didn’t know why it was there. When the ventilation system is running, it creates a positive pressure inside your home. This vent is designed to keep the pressure equalized.
Before you can troubleshoot your ventilation system, first you need to determine if you have a Standard Blend Air II system or a Deluxe Blend Air II system. Looking at the sticker on your control box will usually tell you which system you have.
Standard Blend Air II Troubleshooting
Much simpler than the Deluxe Blend Air II, the Standard Blend Air II basically brings air into the home from a vent on the roof by opening a damper. Unless the furnace blower is running, the damper remains closed.
If your Standard Blend Air II system isn’t working, the problem will generally be the relay or damper motor. The relay is located inside the Standard Control Box. The damper motor holds the damper open allowing air to come inside the furnace from the vent on the roof. Since there are no alarms, the only way you will know if the standard system is not working is by a visual inspection of the damper. If the damper does not open when the furnace blower is running, the system is not working.
Follow these steps to troubleshoot:
1) Verify system doesn’t work: If you are not comfortable with working with electricity and using a meter, please hire someone to troubleshoot and repair your Standard Blend Air II system. At the thermostat on your wall, set the ventilation or fan switch from ‘Auto’ to ‘On’. This should start the furnace blower motor. Remove the filter on the air supply tube located at the top of the furnace. Look up into the tube. If you see the damper open, your system is fine. If the damper is closed, the system is not fine so continue to step 2.
2) Check for power: The Standard Blend Air II should be receiving 24 volts to the relay and 120 volts at the damper motor. First check for 24 volts. If that’s OK, then check for 120 volts at the motor. If the motor isn’t receiving 120 volts, replace the relay. If the motor is receiving 120 volts, replace the damper motor.
Deluxe Blend Air II Troubleshooting
The Deluxe Blend Air II system is more complex than the Standard Blend Air II because it includes an upper and lower control board as well as a blower motor on the roof that ventilates moisture from the attic. Like the standard system, the Deluxe also has the damper assembly.
The Deluxe Blend Air system runs a cycle of 4 hours on and 4 hours off. Unless the furnace blower is running, only the the blower on the roof will run, ventilating moisture from the attic to the outside.
Whenever the furnace blower is running, the damper motor is energized opening the damper and allowing fresh outside air to enter the furnace. If the roof-mounted blower isn’t already ‘ON’, it too will be activated.
For the most part, you won’t have any idea if a problem exists with your Deluxe Blend Air II system unless you here the alarm beeping from the control box usually located in or near your furnace. Besides the alarm, the control box will also flash a red light indicating trouble.
If you have trouble, the following steps will help you figure out what’s wrong. Normally the problem is a bad control board or motor. To troubleshoot you will need a meter that reads both A/C and D/C volts. If you are not comfortable with understanding and using an electrical meter, please hire a competent technician to troubleshoot and repair the system for you. Otherwise figuring out what’s wrong isn’t all that difficult for the average do-it-yourselfer. But if you don’t follow the troubleshooting steps exactly as outlined in this article, you could easily diagnose the problem wrong and pay for parts you don’t need.
1) Verify power: Shut power off to furnace at breaker panel. Remove the Deluxe Blend Air II control box from the wall and turn it around so you can access the lower control board. Remove the red and yellow wires from the board. In earlier models, the yellow wire may be black. Turn the power to the furnace back on. With your meter set to A/C volts, touch the probes of the meter to the red and yellow (or black) wires. If you are getting a reading of 24 volts, you have power. If not, then your problem is not the blend air system. Shut power back off to the furnace and reconnect the wires to the lower control board. Check that the control cable (plug with 4 wires) is plugged into the board and hasn’t come loose. Turn power back on.
2) Verify if attic fan runs? Unplug the 4-wire adapter from the lower control panel. This should cause the attic fan to immediately start running. If you can’t hear the fan, first verify that a breaker to the attic fan is not tripped. This may be labeled as Blend Air in your breaker panel, or in some instances, power to the fan is on the same breaker as your ceiling lights. You then may need to climb up on the roof and listen for the fan. If the attic fan is not running, jump to step 5. If the fan is running, that means the upper control board and attic fan motor are working fine so continue to step 3.
3) Check lower control board: The lower control board is located inside the Deluxe Control Box. This is the same box and board where you just verified in step 1 that you were receiving 24 volts. Do the following checks:
Test 1: Power on the furnace and be sure both switches on the control box are ‘ON’ (you should hear beeping). With your meter set to D/C volts, touch the red and black wires of the 4-wire plug (see illustration). DO NOT ACCIDENTLY SHORT ANY TWO WIRES AS IT WILL BLOW THE BOARD. Your meter should show 30-36 DC Volts. If not, replace the board. If your doing the reading like the illustration shows, push hard enough on your test probes to ensure they make contact.
Test 2: In this test you are testing for voltage while the attic fan is or isn’t running. Because of the 4-hour on and off cycle, it can be hard to tell when the attic fan is actually suppose to be running. So on the lower control board, look for a jumper that says ‘test’. Move the jumper from ‘run’ to ‘test’ by lifting up and putting it back down 1 pin over. This will change the 4-hour ‘ON’ and ‘OFF’ cycle to a 30-second ‘ON’ and ‘OFF’ cycle. Be sure power is off to the furnace before moving the jumper.
With the jumper moved, you should now hear the fan turning on and off every 30 seconds. With the meter set to D/C volts, put the test leads on the black and green wires. You should get a reading of 30-36 volts DC when the attic fan is ‘ON’ or running, and zero volts when the fan is ‘OFF’ or not running. Likewise, when you touch the red and green wires, you should get no voltage reading when the attic fan is ‘ON’ or running, and 30-36 volts DC when the fan is ‘OFF’ or not running. If you don’t get these readings, most likely you will need to replace the lower control board, but continue with the troubleshooting steps to doublecheck the rest of the system.
4) Check the motorized damper: If the lower board checks out OK, next is to verify that the motorized damper works. First remove the screen at the end of the supply tube. Look up and you can see the damper. A damper is a door that opens and closes. Be sure both switches on the Deluxe Control Box are turned to ‘ON’. With the furnace ‘ON’ but the furnace blower not running (set fan switch on thermostat to ‘Off’ or ‘Auto’), the damper should be shut. Turn the furnace blower ‘ON’ by moving the fan or ventilation switch on the thermostat to ‘ON’. Then be sure both switches on the Deluxe Control Box are still turned to ‘ON’. You should hear some beeping again. If the damper opens, your damper motor is fine. If the damper does not open, verify that it is receiving 24 volts. If power, replace the damper motor.
5) Verify upper control board and attic fan: If you’ve verified in step 2 that your attic fan runs, skip to step 6. Otherwise climb up on roof of home and locate the attic fan. The attic fan will be inside a metal vent and not too far away from the furnace chimney. Remove three screws from the bottom of the metal vent and lift off to expose the attic fan. Go back in the house and disconnect the 4-wire plug from the lower control board. Climb back up on the roof and see if the attic fan is running. If the fan is running, this indicates that your attic fan and upper control board are OK. If the fan is not running, doublecheck your home’s electrical panel that there’s not a separate breaker for the Blend Air system. If so, make sure the breaker is ‘ON’. Sometimes power to the attic fan is the same breaker as your ceiling lights. If attic fan still is not running, reconnect the 4-wire plug and go to step 6. If it is running, reconnect the 4-wire plug and turn the ventilation or fan switch to ‘Auto’ on the thermostat and jump to step 7.
6) Verify power to attic fan and checking upper control board: Meter should be set to A/C volts for these tests. Climb up to roof and verify that 120 volts to black and white wires coming into the box. If power, then verify 120 volts by touching the two terminals marked ‘MTR’ on the upper control board. If 120 volts, replace the attic fan motor. Again, DON’T SHORT ANY TWO TERMINALS OR IT MAY BLOW THE CONTROL BOARD.
If no power at the MTR terminals, then recheck the lower control board as explained in Step 3. If still no power to the MTR terminals and the Deluxe Control Box is beeping and the red light is flashing, then replace upper control board.
If no power to the MTR terminals and there’s no beeping and flashing red light from the Deluxe Control Box, then replace the lower control board after again verifying power as explained in Step 1.
7) Attic fan never stops running: As you’ve read earlier, the attic fans runs a cycle of 4 hours on and 4 hours off. But if you feel it’s not stopping at all, you can do the following tests:
Test 1 – Check for 24 volts to the lower control board. If 24 volts A/C isn’t present, the fan motor will run constantly. This could be as simple as a loose wire, or one end of the 4-wire plug is loose. The 4-wire plug connects to both the lower and upper control boards. It doesn’t matter which end is plugged into which board.
Test 2 – One way to simulate 4 hours on and 4 hours off is to move a jumper socket from test to run in the lower control board. Be sure to shut power off to furnace before moving the jumper. Now instead of running 4 hours on and 4 hours off, the attic fan will run 30 seconds on and 30 seconds off for test purposes only. If the fan still continues to run (not stopping after 30 seconds), then recheck lower control board as instructed in #3. Tip: when checking the lower board, check the 30-36DC harness voltage from the end on the roof that connects to the upper board (see Test 3 below). If you are getting proper voltage at that end of the harness, then replace upper control board. If not, then replace the harness and/or lower control board.
Test 3 – If the upper board is not getting a signal from the lower board, the attic fan motor will run non-stop. This is the same as unplugging the 4-wire harness. The upper board not receiving a signal (as noted in step 3) is likely caused by a defective lower board. But do not rule out the fact that the end of the harness connecting the upper and lower board could be corroded or defective. Check both ends and replace if questionable. When installing a new harness, add some special electrical grease to the pins to help combat corrosion.
Misc Items – Here’s a few more things you should know about your Deluxe Blend Air II system:
- The attic fan won’t start running until about 1 minute after the damper opens (unless it’s in the 4-hour ‘ON’ cycle).
- On the Deluxe Control Box, a lit amber light indicates that the damper is open.
- A lit green light indicates that the attic fan is running.
- A flashing red light indicates that the attic fan is not running.