Trane xv80 3 blinks

hvac

Trying to be as thorough and concise as I can, zero experience with hvac.

I have a year 2002 Trane xv80 that is giving me the three blink code, which indicates a pressure switch issue. I disconnected both the low speed and high speed switches, blew into them, and they seem to be making the right kind of clicking noise as I blow or suck. Kind of a cluck-cluck noise.

When I power up the furnace, the main blower starts to circulate are thru the ducts. However the inducer motor is not kicking in after 30 or 45 seconds which by memory is when it should kick in, followed by the igniter. My theory is if the inducer will not spin, then the pressure switches sense inadequate draft and they will then not allow the igniter to ignite, which in turns means no gas will flow and burn, and thus no heat.

I have installed a new flame sensor only because I cleaned it last year and it seemed to solve the problem. However, it may have been a coincidence. But, at approx $12 it was worth a shot. I think the igniter is OK, it ignited a few times over the past few days as I have been troubleshooting, butno longer will ignite.

I unplugged the inducer motor – three wires in the plug, a fourth green is external and goes to a grounding terminal. I put the multimeter on the inducer plug and have continuity. I then inserted the probes into the plug coming from the circuit board and checked voltage after starting the furnace. Nothing registered after a couple minutes of watching, but I may have been doing it incorrectly

Looking for advice. Is there a way to tell if the inducer motor works? I can insert a screwdriver and the fan blade spins. I am not opposed to removing it altogether. Or is there a way to test the circuit board to determine if it is sending voltage to the inducer and if yes, how much should it send and where should I place the probes?

Or would disconnecting the clear plastic tubes from the pressure switches fool the board into thinking all and allow the inducer to go? I am not opposed to ordering parts, just want to know what to replace.

Best Answer

The normal sequence of operation is:

  1. Thermostat calls for heat.
  2. Control module runs self check, and verifies 1st stage pressure switch is OPEN, and limit switches are CLOSED.
  3. Draft blower is energized.
  4. 1st stage pressure switch closes.
  5. Igniter warm up begins (17 seconds).
  6. Gas valve opens.
  7. Flame sensor confirms ignition within 4 seconds.
  8. Delay to FAN ON begins (45 seconds).
  9. FAN ON delay elapses, and blower motor is energized.

It sounds like you're having a problem at step 3. Where either the control module is not energizing the draft motor, or the draft motor is dead.

I'm not familiar with your specific unit, so I'm not exactly sure which speed the control module runs the draft motor at. I would guess that 1st stage uses low speed, but I could be wrong.

To verify the motor is being energized, follow this procedure.

WARNING: You'll be working on live equipment. If you're not comfortable with this, please contact a local licensed professional.

  1. Turn power off to the unit, using either the breaker, or the serviceman's switch.
  2. Remove the wire harness from the draft motor.
  3. Restore power to the unit, and trigger a call for heat.
  4. After a delay, measure the voltage between the white IND-N pin (pin 3), and the red IND-LO pin (pin 2) on the inducer motor wire harness.
  5. Measure the voltage between the white IND-N pin (pin 3), and the black IND-HI pin (pin 1) on the inducer motor wire harness.

You should measure line voltage (~120 volts) between the white wire, and one; or both, of the colored wires. If you don't, the problem is with one of the other limits or the control module. If you do, the problem is likely with the motor.

You mentioned that the blower motor is starting, as soon as the thermostat is calling for heat. If this is the case, that could point to an open limit switch. As the blower should not come on until after ignition, during normal operation.

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