Purpose
Provide guidance for the operation and troubleshooting of modulating hot gas reheat provided by Trane Creative Solutions featuring Sporlan IB-G control boards.
Tools Required
Basic hand tools/multimeter
Minimum of three high pressure gauges
Tracer TU (UC & Symbio controlled units) or Rover (MP controlled units)
Hot Gas Reheat/Unit Performance
See the modifications supplemental IOM for more information before getting started. Standard charging values for subcooling/charging curves do not apply when a unit is operating in hot gas reheat mode but can be applied when operating in cooling mode. When the system is operating properly, extra charge is stored in the hot gas reheat coil. Standard charging procedures cannot be used in applications that include a liquid receiver.
Confirm the circuit is maintaining 5-15 deg F of superheat at the compressor(s) in full cooling and hot gas reheat after 10-15 minutes of operation.
Hot gas reheat coil temperature rise can give you an idea on how well the circuit is performing. The unit submittal will list what the expected temperature rise should be. To check the temperature rise:
- Ensure the indoor fan(s) are operating at max speed
- Run the unit in 100% cooling for 10-15 minutes and record the discharge air temperature.
- Run the unit in dehumidification mode for 10-15 minutes at the hot gas reheat max opening percentage and record the discharge air temperature.
The difference between the two values is the temperature rise. Indoor fan airflow, entering air temperature to the outdoor and indoor coil (evaporator for cooling mode) will impact coil temperature rise.
Modulating Valve Troubleshooting
Attach high pressure gauges to the service ports shown in the red circles below.
Note: This piping serves as an example only. Actual refrigeration components such as the number of compressors will vary depending on your application.
The modulating valves operate inverse of one another. When the unit is not operating in dehumidification, the outdoor coil valve (OD COIL VALVE) will be 100% open and the reheat coil valve will be 0% closed. When the unit calls for dehumidification, the outdoor coil valve will close and reheat coil valve will open proportionally to balance the flow of discharge gas to each coil.
The reheat coil valve max opening position is limited based on unit application. The limitation is in place due to the hot gas reheat coil not being sized to reject the total amount of heat produced by the refrigeration circuit. The supplemental IOM will state what that limitation is.
The best method for testing flow through the modulating valves is to monitor pressure differential across each valve. Attach high pressure gauge at the common discharge line service port after the compress and attached additional gauges directly downstream of each valve. There is not a set pressure drop across each valve. You will read a large pressure drop if a valve is expected to be closed and minimal drop when the valve is open. The valves make an audible noise when driven open/close and produce a slight vibration that can be felt on the valve body. When the unit is first powered up, the valves perform an auto calibration. This is a good opportunity to check their initial operation when feeling for valve vibration.
Liquid Line Solenoid / Check Valve Troubleshooting
Applications will include a reheat liquid line solenoid valve, a check valve or a combination of both. With the reheat modulating valve commanded open, the solenoid must be powered to open which allows refrigerant to flow through the coil. If the valve fails to open, the circuit may experience symptoms of low charge because refrigerant will stack in the reheat coil. In the event the valve or check fails to open, your liquid line temperature will be colder leaving the reheat coil vs leaving the outdoor coil at a 50% modulating valve command. When observing the discharge pressure differential across the reheat valve, you likely won’t notice a pressure drop, but the line temperature will be cooler than expected. You may also notice high discharge pressure due to lack of flow through the reheat coil.
If you suspect the reheat liquid line solenoid valve restriction, check the coil voltage and continuity. For check valve applications, tap on the valve to see if you can unstick it.
IB-G Boards Troubleshooting
Power to the unit must be off prior to making any changes to avoid damaging the control board!
If suspect a problem arises with the IB-G board, it is recommended to revisit the wiring first to ensure proper wire location on the terminals and that all wires are installed and tightened accordingly.
The outdoor coil and reheat coil valves have their own control boards to convert an open/close VDC signal from the programmable control output (Symbio/UC/MP Control) to a stepper signal to each valve. You will read 0-10 VDC to S+ and S- terminal of the IB-G board when the reheat valve is commanded open.
The Reheat Valve Close output from the programmable control is wired to CLS & REF on the IB-G board. The output will be set to closed when there is no call for the hot gas reheat and is designed to force the Reheat Coil Valve shut and will ignore the vdc input signal at S+ and S-. There are no voltage checks for the CLS & REF inputs at the IB-G. To test operation, you must remove the wiring from the IB-G board and check continuity from the control output.
Sporlan IB-G
The Sporlan IB-G boards is a universal board that’s configured with dip switches based on the valve selection.
Refer to the as-built supplied with unit for the appropriate dip switch settings. The as-builts show the dip switch setting on the **Parameters** block. Confirm there is a jumper across the 0-10V pins.
The IB-G board has LED feedback that can be used for troubleshooting purposes.
The RED LED is a status LED and will be on when that IB-G has power.
The YELLOW LED is the Close Valve LED; it will only be on when the valve is fully closed.
The GREEN LED is the Valve Open LED and will flash in different sequences depending on valve position.
- One flash for valve positions >0% and including 10%
- Two flashes for valve positions >10% and including 20%, etc.
- LED will remain on when the valve is fully open
Modulating Valve Troubleshooting
Power to the unit must be off prior to making any changes to avoid damaging the control board!
There are no voltage tests available from the IB-G control board output to each valve, but the resistance of the motor windings may be tested. Resistance can be checked only with the wires removed from the IB-B board. There are different resistance values depending on the vendor part number installed. See the side of the valve body to find out what valve is installed.
CDS-9 and CDS-17 valves, the resistance should be 75Ω ±10% at 71°F (21.7°C)
CDS-2 and CDS-4 valves, the resistance should be 100Ω ±10% at 71°F (21.7°C)
Measure the resistance between the green and red leads. This value should be within ±5% of the resistance between the black and white leads.
Measure the resistance from any lead to the valve body. Resistance should be infinite (open)
WARNING:
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.