The thermostat jumper between Rh and Rc bridges the heating and cooling power supplies in many systems. Understanding when to use this jumper, how to install or remove it safely, and what issues can arise helps maintain reliable climate control. This guide explains Rh and Rc, typical scenarios for bridging, and practical steps for safe setup and troubleshooting.
Overview Of Rh And Rc On Thermostats
Most heating, ventilation, and air conditioning (HVAC) thermostats use separate Rh (heating) and Rc (cooling) power terminals. In systems with a single transformer, a factory-installed jumper connects Rh to Rc, providing a common power source for both heating and cooling functions. In systems with separate transformers, the jumper may be removed to prevent backfeeding and potential equipment damage. The Rh terminal typically powers the heating system, while Rc powers the cooling system.
When To Use A Jumper Between Rh And Rc
A jumper between Rh and Rc is typically present by default on many single-transformer systems. It should be present if the thermostat expects a single 24-volt power source for both heat and cool controls. If a thermostat is designed for a single-transformer system but the jumper is missing, the thermostat may fail to power properly, resulting in nonfunctional heating or cooling. Conversely, if separate transformers exist and the jumper is left in place, power can backfeed between circuits, risking damage to equipment or a safety hazard. Always consult the HVAC equipment manual or a qualified technician to determine if a jumper is appropriate for a given system.
How To Safely Connect Or Remove A Jumper
Safety first: disconnect power to the HVAC system before handling thermostat wiring. Steps include:
- Turn off the circuit breakers for the furnace and air conditioner.
- Remove the thermostat cover to access the wiring terminals.
- Confirm whether the system has one or two transformers by inspecting furnace and air handler wiring or consulting the installation manual.
- If the system uses a single transformer and Rh and Rc are separate on the thermostat, install the jumper wire between Rh and Rc. Ensure the jumper is securely seated across the two terminals.
- If the system uses two transformers, remove the jumper to prevent backfeeding. Do not force a jumper onto two terminals if it’s not required by the design.
- After making any changes, reattach the thermostat cover, restore power, and test whether heating and cooling operate correctly.
Practical notes:
- Use a small, compatible jumper (often included with the thermostat). If replacing, verify the new jumper matches the thermostat model.
- A loose or corroded jumper can cause intermittent power loss; reseat firmly if issues arise.
- Do not modify wiring beyond the jumper unless you have the appropriate electrical training.
Common Issues And Troubleshooting
Several problems can surface around Rh and Rc configurations:
- Heating or cooling not turning on even with power: Check whether the jumper is present if a single-transformer design is specified. Ensure the thermostat is configured for a single transformer in its settings.
- Tripping breakers or buzzing sounds: This may indicate backfeeding or a miswired transformer. Power down and recheck wiring or consult a professional.
- Thermostat displays but does not respond: Confirm the thermostat is compatible with the HVAC system and that Rh and Rc are properly connected. Reboot the thermostat by removing and reinserting power if supported.
- Uneven temperature: If the system favors one function, ensure the corresponding transformer and wiring are healthy and that the jumper is not causing unintended cross-feed.
Choosing The Right Thermostat Jumper Wire
Selecting the correct jumper involves matching the thermostat model and system configuration:
- Check the thermostat installation manual for recommended jumper type and placement.
- Use a jumper that fits snugly on the Rh and Rc terminals without interfering with adjacent wires or screws.
- For heat-only or cool-only setups, a jumper may be unnecessary if the thermostat is designed for a single transformer.
- In cases of dual transformers, do not install a jumper unless the manual explicitly permits it for the specific model.
Additional considerations:
- Color coding is not universal; rely on terminal labels rather than wire color to identify Rh, Rc, W, Y, G, and C connections.
- If upgrading to a smart thermostat, verify whether the new model requires or omits a jumper and how it handles power sharing between heat and cool circuits.
- Routine maintenance should include periodic inspection of thermostat wiring and the transformer health to prevent power issues.