987M

24 V fuse. Evolution still has a 24 V secondary.

1. 1 Find the 24 V short before you replace the fuse

   On Bryant 987M an open IFC fuse is a short on W, Y, G, HUM, EAC, or a data pair landed on 24 V. Unplug the thermostat / data harness first. Short on HUM/EAC, valve, or 24V landed on ABCD.

   Expect: Fuse out. 24 V transformer still good. Harness isolated.

2. 2 Replace the fuse with the harness off

   New fuse, harness still off. If it holds, the short is in the field wiring or accessory. Plug one circuit back at a time (W, then Y, then HUM/EAC).

   Expect: Fuse holds with harness off. Dies when the shorted lead lands.

3. 3 If it blows with the harness off

   Short is on the Bryant 987M IFC or the gas-valve harness. Unplug the valve and try once more. Repeat blow with valve unplugged = IFC.

   Expect: Do not keep feeding fuses into a welded valve coil or a burned IFC trace.

Modulating inducer did not hit the band for the commanded rate.

1. 1 Prove inducer and the live code

   Do not pull power — that clears the Bryant 987M active code. Write 31 / 42. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Vent, trap, inducer, transducer/hose — do not ohm a ‘low’ and ‘high’ switch that are not there.

   Expect: 120 VAC at the inducer on a heat call. Wheel turning.

   If fail: 120 VAC missing → IFC / door switch / incoming power. Voltage + dead motor → inducer.

   If pass: Inducer running + this code → trap, hose, switch, vent (step 2).

2. 2 Trap, collector, and the hose

   A drowned 96% trap will not make collector pressure. Pull the trap, flush it, confirm the collector box and inducer outlet are not full. Hose cracked, off the port, or full of water fakes an open switch. 42 = inducer RPM out of the commanded band.

   Expect: Trap flowing, hose dry and downhill, ports not swapped on a two-switch board.

3. 3 Switch ohms, then vent load

   Ohm the pressure switch: NO, must close when that inducer speed is making the collector setpoint. If the switch is good, walk the PVC — bird screen, ice, long 2" run, wind, shared chase.

   Expect: Switch closes on known draft. Vent unrestricted.

   If fail: Replace the open switch only after the vent and trap are proven.

   If pass: Switch closes on draft and the code stays → IFC input.

Airflow or rollout. 13 is the hardened 33.

1. 1 Treat this as flame outside the exchanger

   Do not reset the Bryant 987M rollout and walk away. Write the code, kill the call, and look for flame at the burners, crossover, and vestibule before you do anything else.

   Expect: No flame outside the exchanger. Burners seated. Crossover lit.

   If pass: Still inspect secondary / flue / condensate before you reset.

2. 2 Secondary, condensate, and flue

   Blocked secondary, drowned collector, or a plugged flue pushes flame out the front. Pull the inducer/collector look, confirm the trap is flowing, and check PVC/vent. Evolution heat CFM, filter, coil. Rollout is manual reset.

   Expect: Dry collector, open flue, trap clear.

3. 3 Reset only after the cause is fixed

   Manual-reset rollout. Recurring rollout on Bryant 987M is a CO / fire call — cracked primary, misaligned burners, or a failed secondary. Confirm CO in the space before you leave.

   Expect: One clean cycle after the cause is fixed. No second reset as a repair.

No flame prove.

1. 1 Watch one full try — do not reset

   Write the Bryant 987M code. Watch inducer, HSI glow, valve click, flame, µA. The step that dies is the repair. Resetting only burns another try into a harder lockout. HSI, gas, rod. Then the modulating valve offset — a valve stuck on minimum looks like 34.

   Expect: Call → Prove → Ignition

2. 2 Gas and the valve

   Cock open, inlet pressure, then manifold on the stage that is failing vs the rating plate. 24 VAC at the valve during trial? Coil ohms? A valve that never opens looks like a ‘bad igniter’ if you did not watch the sequence.

   Expect: Inlet and manifold on the plate. 24 VAC only during trial.

3. 3 Flame prove, then the lockout timer

   Glow + valve + no prove → rod, ground, or IFC sense. Prove then drop → µA / PS / limit. Soft lockouts on this family often auto-reset on a long clock — do not sit on resets.

   Expect: Flame sense: µA per this Evolution / 59MN7 door card.

Evolution VS motor not at commanded CFM.

1. 1 Is the wheel free?

   Spin the Bryant 987M blower by hand. Ice, debris, or a seized bearing is not a control problem. Confirm the motor type on this plate — serial ECM, 9-speed tap, or X-13 — before you grab a capacitor. Static, wheel, harness. Do not swap a 926T model plug onto this IFC.

   Expect: Wheel free. Correct motor family for this IFC.

2. 2 Command vs rotation

   Call for G or heat and confirm the IFC is actually requesting CFM (taps, serial, or communicating). Amp the motor. Locked rotor + a good command = motor. No command = IFC / harness / shared data.

   Expect: Command present. Motor amps in range, not locked.

3. 3 Static and the wrong motor

   High static will trip current/limit codes and look like a dead motor. Measure TES vs this cabinet. Wrong horsepower or a leftover memory card after a control swap is the other half of this call.

   Expect: Static on the blower chart. Matching motor / shared-data card.

Wall control or outdoor dropped.

1. 1 Data pair, not 24 V

   On Bryant 987M indoor/outdoor comm is a data pair (AB, S1/S2, U, ComfortBridge, ComfortLink — whatever THIS plate uses). It is not a 24 V Y. Check polarity, continuity, and that nobody landed it on R/C. A/B/C/D, polarity, C present, no 24V on D.

   Expect: Pair continuous, not shorted to chassis, polarity per the diagram.

2. 2 Power both ends, then the outdoor status

   Indoor transformer and outdoor control both alive. Read the outdoor LED / 7-seg. Water in the outdoor control is the usual dead-end after a storm. One Evolution control only.

   Expect: Both controls powered. Outdoor showing a comm or address state, not a blank board.

3. 3 Address / bias, then the control

   Communicating plates need a matching indoor address and sometimes a terminating bias. Swap is last: known-good pair + power both ends + correct address.

   Expect: Indoor sees the outdoor. No comm code after a power cycle.