Overview
All Voyager II RTU's with ReliaTel Controls using only fixed speed compressors, utilize two fixed speed condenser fans. The operation of the condenser fans is based on special control logic is designed to provide proper condenser head pressure control at different ambient conditions. With normal operation, either one or both fans will be operating depending on the outdoor temperature.
On all of these units (except heat pump), Condenser Fan 1 (ODF1, fan closest to the control panel, drawings will label as ODF2) is wired to operate through a set of parallel wired auxiliary contacts on the side of each compressor contactor. ODF1 is wired this way with the intent that if any compressor is running, this fan is also on. See drawings in trouble shooting section below.
Condenser Fan 2 (ODF2, fan furthest from the control panel, drawings will label as ODF1) is controlled through RTRM relay K7 (terminal J3-6). The RTRM will stage this fan on/off based on the Outdoor Temperature.
Sequence of Operation for Non-Heat Pump
Low Ambient Operation
Control logic resides in the RTRM module. When the outdoor ambient drops below 60 degrees the second condenser fan will be turned off. When the outdoor temperature reaches 65° the fan will once again restart.
Windmill Logic
When only one condenser fan is running, the second fan will windmill backwards. This is caused by air being drawn in through the opening of the fan orifice which bypasses the condenser coil. If the windmilling is fast enough and the condenser fan is energized, it can actually start and run in the reverse direction. To prevent this, when there is a call for the second condenser fan to start, control logic forces the first condenser fan to shut off for seven seconds to allow the second fan to slow down. After seven seconds, both the first and the second condenser fan will restart. Because the contactors that provide power to the condenser fan are also the same ones used to power the compressors, both compressors (if the second compressor is running) will also shut down during the seven second interval. When the fans restart, the compressor will also restart.
This Windmill Logic is enabled on the RTRM at pin J3-5 not being connected (Open). Grounding this terminal will disable the Windmill Logic. All Voyager II units have this feature enabled (J3-5 Open) from the factory and some older Voyager II units may have a wire that can be connected to ground to disable this feature.
Sequence of Operation for Heat Pump
Low Ambient Operation
The sequence of operation is the same as a cooling only unit, the difference on heat pump is that the 24vac that is used for the common power for the compressor contactor auxiliary switches is controlled by the RTRM Relay K8 (terminal J2-6). For cooling and heating efforts, Relay K8 is closed at all times so that any time a compressor is running, ODF1 is on. The only time Relay K8 opens is during defrost efforts or when there is no call for compressor operation.
Windmill Logic
Windmill Logic is the same on heat pump.
Troubleshooting
Cooling Only Unit
ODF1
For ODF1 issues, the power should be checked from Transformer 3 (TNS3). TNS3 supplies 24vac through Control Terminal Block 2 (CTB-2) for both condenser fans, Compressor 2, Compressor 3, 2-Speed fan relay operation, both heat high limits on gas heat units and electric heat.
Another common issue is the auxiliary wiring is not connected correctly during contactor replacement or troubleshooting, see below for correct wiring between CTB-2 and through the compressor auxiliary contacts
*Drawing simplified for detail/explanation purposes
ODF2
For ODF2 issues, the same troubleshooting should be done checking power from TNS3, but if power is good and ODF2 is not running, it could be due to the low ambient sequence. Check the Outside Air Temperature (OAT), if below 60°F, ODF2 should be off. Also understand that once ODF2 is disabled due to low OAT, it is not re-enabled until the OAT > 65°F.
If the OAT > 65°F and TNS3 power is good, disconnect the OAT sensor from RTRM J8, if the fan comes on, the RTRM thinks the OAT < 60°F. This could be due to:
- A faulty sensor
- Troubleshoot sensor resistance using a 10k Type II thermistor chart
- OAT close to or has not increased above 65°F
The last item to check for ODF2 if disconnecting the OAT sensor does not work, is to check for a connected Building Automation System (BAS) that may be providing a value that is not accurate. This is a common issue on large sites where they use a central weather station for the entire site and either it is reading differently that what the actual temperature is at the RTU or has failed and is passing a null value that is low, but technically still in range for the RTU.
This issue can cause multiple issues with the unit control including head pressure trips from not running ODF2, improper defrost operation on heat pumps and unexpected economizer operation.
We do not recommend supplying the RTUs with a BAS OAT value and prefer the unit sensor control it. In many instances, this is done to have tighter control over when the unit economizes, we recommend that the BAS Enable/Disable Economizer operation directly using their own logic instead of providing the OAT to the unit.
A failed relay is always a possibility and if all the testing above checks out, it is a good possibility. Verify that 24vac is present on RTRM J3-1 and if so, power should be present on J3-6. If not and all testing is complete above, Relay K7 has possibly failed.
Heat Pumps
ODF1
Troubleshooting for ODF1 is the same on heat pump, except the 24vac comes from the RTRM, but it ultimately is still provided from TNS3 via CTB2, it is just controlled by Relay K8 on the RTRM.
If the unit is in cooling or compressor heat and not in defrost, RTRM Relay K8 should be closed and ODF1 should be running. If it is not, check for 24vac on RTRM J2-10 and J2-6. If power is present at J2-10 and the operation of the unit should be calling for ODF1, Relay K8 may have failed.
ODF2
Troubleshooting for ODF2 on heat pump is the same as a cooling only unit. The only time ODF2 should be off is when:
- OAT < 60°F and has not increased above 65°F
- Unit is in defrost
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.