On RTRM version 4.0 or higher, the green system LED2 on the RTRM module can provide a quick visual indication of the presence of certain diagnostics. If the green LED2 on the RTRM is blinking with two ¼ second blinks every two seconds, one or more diagnostics are present.
If the service technician sees the RTRM fault indication, the next step is to check for diagnostics using a DC voltmeter. Terminals located on RTRM J6 are used to decipher the active diagnostic.
J6-6 = Common
J6-7 = Heating
J6-8 = Cooling
J6-9 = System
J6-10 = Service
Measuring J6-6 against any of the other listed terminals will indicated the status of that feature of unit. The chart below shows the different voltages that can be measured based on the connected zone sensor type.
|Thermostat or mechanical zone sensor w/o indicators or no sensor attached at all||Programmable Zone Sensor w/ indicators (BAYSENS119)||Mechanical Zone Sensor w/ indicators|
|ON||32 VDC +/- 10%||26 VDC +/- 10%||2.0 VDC +/- 10%|
|OFF||0.75VDC +/- 10%||0.75VDC +/- 10%||0.75VDC +/- 10%|
|PULSING||20 to 30 VDC||14 to 30 VDC||14 to 30 VDC|
Note: At the bottom of the meter display, the analog bar will pulse back and forth. Some meters do not have this extra feature.
Service - RTRM-J6-10
What the Readings Mean
Clogged filter switch has been closed for at least 2 minutes, indicating a clogged filter. This example illustrates what would be seen if the unit did not have a zone sensor with indicator LEDs, such as would be the case with an ICS system.
– Clogged filter switch is in open position or no switch is installed.
– Fan fail switch (if installed) has opened (3 to 25 tons) or closed (27.5 to 50 tons) within the first 40 seconds, proving that the supply fan has started.
– Fan proving switch/fan fail switch (FFS) has failed to open (3 to 25 tons) or close (27.5 to 50 tons) before 40 seconds. During this condition, the unit will run for 40 seconds and then stop. Only the fan will run during the TEST mode, except during the first 40 seconds.
– Condensate pan switch is actively closed or has closed 3 times during a 24 hour period.
What the readings mean
System is powered up. This output should be on whenever the green RTRM System LED is on. Incidentally, this LED may flicker as part of its normal function on older version boards.
If 0 Vdc is seen, the RTRM does not have power, the output wiring is shorted, or there is an internal failure. Remove any wires connected to this terminal and check again.
Unit is in the TEST mode. Also during the TEST mode the System LED will pulse on and off. This output does not provide any diagnostic information, but is a good place to confirm voltage readings taken are consistent with what should be seen on other outputs.
What the readings mean
System is in the cooling mode and actively cooling. The unit could be economizing or have one or both compressors on. If the unit is a heat pump, the reversing valve is energized as well.
System is not actively cooling. It may or may not be in the cooling mode.
Note: Any controls.
This indicator can mean one or more of the following:
• CC1, CC2, or CC3 opens during cooling, or is open when a call for compressor occurs. The unaffected circuit will still run. With RTRM version 4.0 or greater, CC1, CC2, or CC3 circuit must open on 3 consecutive cycles. On the 4th trip, the unit will lockout.
• CPR1 disable or CPR 2 disable input has opened during a compressor cycle each time a compressor starts (within the first 3 minutes) for 3 consecutive cycles. It locks out on the fourth cycle. The unaffected circuit will still run.
• Frostat input is active. (24vac present on RTOM J7-2)
• Zone temperature input failure after a successful input.
• Both heating and cooling setpoint inputs have failed or are not attached (such as when using a two wire sensor on terminals 1 and 2).
The ZSM has failed to communicate for 15 consecutive minutes after successful communication has occurred.
What the readings mean
System is actively heating.
System is not actively heating.
– Gas heat: If any failure occurs such as loss of flame, limit switch trip, flame rollout etc., this indication is present. Further diagnostics are available by examining the ignition module LED. See the gas heat section for detail.
– Electric heat: These units have safety limit switches in the electric heat control circuit. Should a limit switch trip, no diagnostic will occur. the HEAT indication will stay ON.
– Heat pump: Unit is in the EMERGENCY HEAT mode. If the compressor disable circuit or CC1, CC2 circuits create a lockout during heating mode, a COOL FAIL (pulsing) indication will occur, not a HEAT FAIL (pulsing) indication. See COOL indications for details.
HEAT FAIL and COOL FAIL at the Same Time, RTRM-J6-7 and 8 Pulsing Voltage
• Coil temperature sensor is open or shorted (heat pump only).
• Unit has failed to defrost properly (see heat pump section for further details).
• Outdoor air sensor is open or shorted (RTRM version 4.0 or greater).
• Dehumidification unit - RTOM disconnected or not communicating. RTOM will flash once every few seconds.
• Emergency stop input is open (no 2 flash diagnostic present on RTRM).
• Factory installed phase monitor is indicating a fault (no 2 flash diagnostic present on RTRM).
• Entering evaporator temperature failure (on modulating reheat units).
• RTDM communication failure (on modulating reheat units).
• Supply air temperature is invalid and unit is SZVAV, MZVAV, CV with modulating heat or modulating reheat, or supply air tempering is enabled.
HEAT + COOL + SERVICE
Smoke Detector failure active.
Compressor Will Not Run - No Diagnostics
• Frostat™ trip (RTRM v8.0 and later will exhibit diagnostics as described previously).
• Compressor disable input open.
• Unit is economizing, and outside air damper is not yet at 100%.
• Unit is in “heat” mode or “off” mode.
• Tracer® or building management system is preventing compressor operation (demand limit).
Heat Pump - Compressors Will Not Run
• Unit is in the EMERGENCY HEAT mode.
• If the compressor disable circuit or CC1, CC2 circuits create a lockout during heating mode, a COOL FAIL (pulsing) indication will occur, not a HEAT FAIL (pulsing) indication. See COOL indications for details.
MZVAV/VAV unit - Additional Diagnostics
Zone temp input (RTRM J6-1) is open, shorted, or failed during an unoccupied mode. If the unit has a default mode input (jumper from RTRM J6-2 to RTRM J6-4, a valid zone temp input is needed for unoccupied heating, MWU and DWU.
COOL + SERVICE
Static pressure transducer output voltage at RTAM J1-3 is less than 0.25 Vdc. The transducer output is open, shorted, or the transducer is reading a negative supply air pressure.
HEAT + COOL + SERVICE
• Static pressure high duct static trip. The static pressure has exceeded 3.5 inches wc three consecutive times.
• Ground wire on transducer is open.
27.5 to 50 Tons - Additional Diagnostics
If only one diagnostic is present, refer to that diagnostic. If more than one diagnostic is present, refer to combination diagnostics such as COOL + HEAT as appropriate. On a BAYSENS020*, the display will show HEAT FAIL or COOL FAIL or SERVICE (or an appropriate combination) if a diagnostic is present.
• Discharge air sensor (DTS) is open, shorted, or has failed.
• CC1 or CC2 24 Vac control circuit has opened three times during a cooling mode. Check CC1, CC2 coils or any control in series with the coils (winding thermostat, HPC, circuit breaker auxiliary contacts).
• LPC 1 or LPC 2 has opened during the 3 minute minimum “on” time during 4 consecutive compressor starts. Check LPC 1 circuit by measuring voltage from RTRM J1-8 to chassis ground. Check LPC 2 circuit by
measuring voltage from RTRM J3-2 to chassis ground. If 24 Vac is not present, the circuit is open. 24 Vac
should present at these terminals at all times.
• The RTDM Low Pressure Cutout Input (RLP) will be ignored for the first 10 minutes of compressor run time on the reheat circuit. Once active (OPEN), the associated circuit/output will de-energize and not reenergize until the 3 minute off timer is expired and the input has cleared. If the reheat LPC trips 4 times in any mode after the circuit has been energized for 10 minutes, dehumidification will be disabled (all compressors off) and the reheat circuit will be locked out.
The supply fan proving switch (FFS) has failed to open within 40 seconds after the fan starts or has closed during fan operation.
HEAT + COOL
• RTDM communication failure.
• Entering air temperature evaporator temperature sensor failure.
2 Flash Blink Code - RTRM Only
• Outside Air Flow Transducer (Traq) reading outside of normal operating range or bad calibration solenoid.
• Space Pressure Transducer (Statitrac) reading outside of normal operating range or bad calibration solenoid.
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.
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