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Case #313: Troubleshooting a Cool Problem (Failure) Diagnostic
This information applies to:   VOYAGER UCP 3-25, VOYAGER UCP 27.5 - 50

If certain unit problems or conditions exist, the Unitary Control Processor (UCP) micro control has the capability of creating a “cooling diagnostic” indication. This diagnostic may be displayed on a zone sensor, building management system (Tracer, Tracker, Varitrac) or tested at the unit’s LTB-1 (Low Voltage Terminal Board).

If a mechanical Zone Sensor Module (ZSM) is installed, the “cool” LED (if present) will be blinking. If a programmable ZSM is used, a cool fail will be indicated on the display. If no zone sensor module is used (or this feature is not used), conduct the following test at the LTB-1.

At the LTB-1, a pulsating DC voltage (1 – 32 volts DC) between terminal 8 to ground will indicate a cool fail diagnostic.

CTI NOTE: If a Conventional Thermostat Interface (CTI) is installed, the diagnostic pulsating voltage must be read from J7-5 on the UCP to ground instead of reading the voltage at the LTB-1.

Step #1:  Location of the LTB

The LTB is located right beside the control box.
Voyager 3-50 Location of UCP


Step #2:  Testing for Cooling Diagnostic

A cooling diagnostic occurs when a pulsating (1 – 32 volts AC) exits at LTB-1 terminal 8 to ground. To get the best voltage measurement, temporarily remove any field wire connected to terminal 8.
Ipak General Status Screen 4

The following may cause a cool diagnostic:
  1. Contactor coil circuit problem - If a safety control (like high pressure control) opens to shut down the compressor contactor coil, a diagnostic will occur. This causes a lock out condition and the diagnostic must be reset. The contactor coil circuit looks for a normal coil ampere load ranging from 1/10 to 1 1/10 amp, so if the contactor coil starts to burn out and draws excessive power through the coil, this will cause a cooling diagnostic too. (An ampere load of less than 1/10 amp will also cause a diagnostic)
  2. Low pressure control cycling – Normally, if the low pressure control opens, it will shut the compressor off, but this does not create a diagnostic. After the low pressure control closes, and the minimum time delays have lapsed, the compressor will automatically restart. However, if the low pressure control opens during the first 3 minutes of the compressor operation on 4 consecutive compressor starts, a compressor lock out will occur and cooling diagnostic will be created. The lock out must be reset before the compressor will restart.
  3. Loss of mechanical zone sensor module temperature input (LTB-1 1 & 2) – Without zone temperature input the unit will not heat or cool. To verify a valid zone temperature input, the DC voltage at LTB terminal 1 to ground should be from about 2 to 3 volts DC. To test this circuit further, Testing the Zone Temperature Sensor.
  4. Loss of mechanical zone sensor module set points (LTB-1 2 & 3 and LTB-1 2 & 5) - Without set points, the unit will run using these default set points: 74F cooling, 71F heating. A “cool fail diagnostic” indication will be present, but the unit will run. To check this circuit, Testing the Zone Temperature Sensor.
  5. Loss of communication with programmable zone sensor module – A loss of communication on LTB-1 11 & 12 will give a “cool fail diagnostic” indication. The unit will not run: no fan, no heat, no cool.
  6. Using TCI (Trane® Communication Interface) – When the UCP (Unitary Control Processor) controls are interface with Tracer, Tracker® or Varitrac, a TCI is required. When the TCI is used, a cooling diagnostic may be present, even though the system is operating properly. This diagnostic is to be disregarded on these systems.
  7. Resetting a lockout – If a lock out occurs, remove power to the unit to reset the unit. If this clears the cooling diagnostic, there was a lock out (see A & B above). If the cooling diagnostic immediately re-appears, see B & F.

    Step #3:  General Troubleshooting Chart

    21. troubleshooting Chart "Problem Descriptions and Causes"

    Note: Always verify the unit is operating in the proper "MODE" when troubleshooting.

    SYMPTOM PROBABLE CAUSE RECOMMENDED ACTION
    A. 3-25 Ton - Unit will not operate in the TEST MODE - no fan, cool or heat. 1. No power to the unit. 1. Check line voltage to the unit.
    2. No power to the UCP. 2. Check for 24 VAC from bottom of F1 fuse to system.
    3. UCP fuse (F1) is defective. 3. Check for 24 VAC from top of F1 fuse to system ground. If 24 VAC is not present, fuse is bad.
    B. Goes into TEST MODE runs for 15-40 seconds, then stops: 1. Unit has entered AFF mode 1. See Section 23.7 & 23.8. Check IDM, belt. (Nothing runs)
    2. A TCI is installed and its High-Temp input is open w/DIP sw. #1 ON. 2. Close input or turn switch to OFF if not used. (Nothing runs)
    3. Heat pump only - fan runs 15 sec & stops 3. Polarized plugs not configured correctly - see Section 35.5. (Nothing runs)
    4. Goes into TEST MODE (UCPs LED blinks) but still will not run. 4. Each output - cool 1 & 2, heat - is locked out. Troubleshoot each circuit individually. (Only fan runs)
    C. 27.5 - 50 Ton - Unit will not operate in the TEST MODE No fan, cool or heat 1. See test 1-3 in "A" above 1. See above
    2. Auto Stop input is open 2. Close Auto Stop input; after 5 seconds system will run
    D. Goes into TEST MODE, runs for 40 seconds, then stops. 1. FFS failed to close after 40 seconds. 1. See Section 23.7, 23.8. Check belt, IDM
    2. A TCI is installed and its High Temp input is open w/DIP sw.#1 ON. 2. Close input or turn switch to OFF if not used. For additional troubleshooting information on V3 see IOM.
    E. Unit will not heat or cool but the fan switch operates. 1. ZSM is defective. 1. Refer to Zone Sensor Module troubleshooting, Sections 26 & 27.
    2. Problem in ZSM wiring.

    2. Verify wiring connections between LTB and ZSM.

    F. Unit heats and cools but will not control to setpoint 1. ZSM is defective. 1. Refer to Zone Sensor Module Troubleshooting, Sections 26 & 27.
    2. Unit is over/undersized. 2. Look at Section 40 for more information.
    3. ZSM location poor. 3. Look at Section 40.1 for more information.
    G. CPR1 will not operate, ODM runs 1. Compressor failure.

    1. Test compressor - replace if necessary.

    2. CC1 contator or wiring failure 2. Check wires, terminals and CC1. Replace if necessary.
    H. CPR1 operates, ODM1 will not operate 1. ODM has failed.

    1. Check wires, terminals and CC1. Repair / replace if necessary.

    2. ODM capacitor(s) has failed 2. Repair connection / replace as needed.
    I. CPR1 & ODM1 operates, but ODM2 will not 1. OAS is out of range. 1. Test Outdoor Air Sensor - see Section 28.5.
    2. ODM / capacitor has failed

    2. Repair / replace as needed.

    J. CPR1 and ODM1 will not operate even in the TEST MODE, but fans run OK. 1. CC1 Circuit open. 1. Check wiring, terminals and applicable controls (CCB1, HPC1, & WTL1) see Section 53 "Snubber Circuits".
    2. LPC1 circuit open. 2. Verify 24 VAC input at J2-2 - voltage should always be present.
    3. UCP is defective

    3. Cycle power off, then on, & try TEST MODE again. If compressor runs, it was in a Cool Fail mode. See Section 23.3. If compressor still will not run UCP must be replaced.

    K. ODM 3 and/or 4 will not cycle. 1. OAS 1. Perform OAS Resistance/Temperature check. Replace if necessary.
    2. ODM3 and/or 4 capacitor has failed. 2. Check ODM capacitor, replace if necessary.
    3. Wiring, terminal, or CC2 contactor failure. 3. Check wires, terminals, and CC2. Repair or replace if necessary.
    4. ODM3 and/or 4 has failed. 4. Check ODM, replace if necessary.
    5. UCP is defective. 5. Replace UCP module
    6. ODF2 has failed.

    6. Check for proper voltage and contact closure. ODF2 relay has a 24 VDC holding coil. If voltage is present, replace relay.

    L. CPR2 and 3 (if applicable) will not operate. 1. No power to CC2 and/or 3 coil. Cool Failure Possible. 1. Check wiring, terminals and applicable controls (CCB2, CCB3, HPC2, LPC2, WTL2, WTL3
    2. CC2 and/or 3 coil defective. Cool Failure Indicated 2. Verify integrity of CC2 and/or 3 coil windings. If open or shorted replace CC2 and/or CC3.
    3. CC2 and/or 3 contacts defective. 3. If 24 VAC is present at CC2 and/or 3 coil, replace relay.
    4. UCP is defective. 4. 24 VAC is not present at CC2 and/or 3 coil. Reset the Cool Failure by cycling the service disconnect. Place the unit into Cool Stage 2 Mode, step 4 for constant Volume or step 6 for variable air volume, to ensure CPR2 and 3 Compressor operation. Check input devices in #1 & #2 above, if no controls have opened, and CC2 and/or 3 will not close, replace UCP.
    M. Indoor motor (IDM) will not operate 1. IDM has failed. 1. Check IDM, replace if necessary.
    2. Wiring, terminal, or contactor failure. 2. Check wiring, terminals and F contactor. Repair or replace terminals, or fan contactor F.
    3. ZSM is defective. 3. Place unit in test mode. If the fan operates in the test mode, test ZSM using the appropriate test.
    4. UCP is defective. 4. Check the UCP fan output. Locate P2 connector, which is connected to J2 on the UCP. Find wire 64A (Black) and measure voltage to ground. If 24 VAC is not present on a call for fan, replace the UCP.
    5. Supply Fan Proving (SFP) switch has opened 5. Check SFP and belts, repair or replace if necessary.
    N. No Heat (YC’s CFM will not run, IP warms up, GV is energized. 1. CFM has failed. 1. Check CFM, replace if necessary.
    2. CFM capacitor has failed. 2. Disconnect BROWN wires from capacitor, test, and replace if necessary
    3. Wiring, or terminal failure. 3. Check wiring, and terminals. Repair, or replace if necessary.
    4. Heat relay H 4. Check for line voltage between terminals 1 & 3 on heat relay. If voltage is present, contacts are open. Check for 24 VAC at H coil, replace H if 24 VAC is present.
    5. TNS2 and/or 3 has failed. (460/575 V units only) 5. Check for 230 VAC at TNS2 and/or 3 secondary, between Y1 and Y2. If 230 VAC is not present, replace TNS2 and/or 3.
    O. No Heat (YC's only) CFM runs, GV energizes, IP does not warm up. 1. TNS2 and/or 3 has failed. 1. Check for 115 VAC at TNS2 and/or 3 secondary, between X1 and X2. If 115 VAC is not present, replace TNS2 and/or 3.
    2. Wiring or terminal failure. 2. Check wiring, and terminals. Repair, or replace if necessary.
    3. IGN has failed. 3. Verify presence of 115 VAC at IGN L1 and L2. Check for 115 VAC between terminals PPM4-1 and PPM4-2, and PPM5-1 and PPM5-2 (if applicable) in the gas section. If 115 VAC is present for IP warmup, IGN is OK. If 115 VAC is not present, replace IGN.
    4. IP has failed. 4. With 115 VAC applied to IP, warm up should take place. Cold resistance of IP should be a minimum of 50 Ohms. Nominal current should be 2.5 to 3.0 Amps.
    P. No Heat (YC’s only) GV does not energize, CFM runs, IP warms up 1. Wiring or terminal failure. 1. Verify presence of 24 VAC between IGN PWR terminal to ground, if not present, check wiring and terminals. Repair or replace if necessary.
    2. IGN has failed 2. Verify presence of 24 VAC between IGN VALVE terminal to ground, if not present replace IGN.
    3. GV has failed. 3. Measure voltage between TH and TR on the gas valve (GV). If 24 VAC is present and the GV will not open, replace the GV.
    Q. Low Heat Capacity, Intermittant Heat. (YC's only) CFM runs in LO or HI speed only, or may not operate at all in one speed or the other. 1. CFM has failed. 1. Check CFM, test LO and HI speed windings.
    2. UCP is defective. 2. Check UCP K5 relay. Check for K5 coil voltage at solder joints CR16 above K5 on the UCP. Nominal voltage at the coil is 28 VDC. If 28 VDC is present, COM. & N.O. contacts should be closed, energizing DFM HI speed windings. If 28 VDC is not present, LO speed should be energized through K5 COM. & N.C. contacts. If voltage contradicts operation, UCP has failed
    R. No Heat (YC’s only) "Fan" selection switch on the ZSM is in the "AUTO" position and the fan runs continuously. 1. TCO2 has opened. Heat Failure Indicated 1. System Status Failure Diagnostic Place the unit in the Heating Test Mode, steps 6 & 7 for constant volume or step 8 & 9 for variable air volume and check the complete heating system for failure. Make necessary reapairs or adjustments to the unit.
    S. No Heat (TEs only) Electric heat will not operate. 1. Heater contactor(s) have failed. 1. Check for 24 VAC at AH, BH,CH, and DH contactor coils. If 24 VAC is present on a call for heat, and the contacts do not close, the contactor has failed.
    2. Heater element temperature limit(s) is open. 2. Check line voltage between the element temperature limit terminals located in heat section. If line voltage is present, the limit is open. Repair heating unit, or replace limit(s) as needed.
    3. Wiring or terminal failure. 3. Check for wiring, or terminal failure in control and power circuit. Repair or replace if necessary.
    4. Heater Element(s) has failed. 4. Check element and circuit integrity. Repair or replace as necessary. Replace open elements.
    5. UCP is defective. 5. Check UCP heat outputs. "First stage", locate P1 connector, connected to J1 on the UCP. Locate wire 65E at terminal P1-22, measure between 65E and ground. If 24 VAC is present, repeat #3 above. If 24 VAC is not present, the UCP has failed. "Second stage", Check UCP K5 relay. Measure from the common terminal on the relay to ground, 24 VAC should be present, if not repeat #3 above. If present, measure from the N.O. terminal on the relay to ground. If 24 VAC is not present, the UCP has failed.
    T. Evaporator coil freezes up during low ambient operation. 1. System low on refrigerant charge. 1. Leak check, repair, evacuate, and recharge system as necessary.
    2. System low on air flow. 2. Check return air for obstruction or dirty filters. Check fan wheels, motors, and belts.
    3. Outdoor Air Sensor (OAS) has failed. 3. Check OAS at connector P1 by disconnecting P1 from J1 on the UCP. Check resistance between P1-15 and P1-16, refer to the Resistance versus Temperature chart. Replace sensor if necessary.
    4. FrostatTM has Failed 4. Check Frostat Switch
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