Commissioning: Furnace tips (part 2 of 3)

Short, practical technician tips on commissioning for furnace. Check each one against the manual for your exact model before acting.

Condensate trap priming on first start

Rheem · Condensate drain trap, all 96V installs

The condensate trap is self-priming. It starts dry on the first heat attempt after install or after a long off period. Priming can take several cycles, especially on horizontal installs, because there is less water stored in the collector box.

1. Expect the trap to be dry on the first firing after install or after a long summer off period.
2. Let the inducer run. Water builds in the collector box until it reaches the lower water level sensor.
3. Confirm the trap primes after the heat attempt ends and the inducer shuts off after post purge.
4. If the trap is still not primed, allow up to four heat attempts before deciding there is a fault.

Condensate vent tube height options

Rheem · Condensate vent riser on all 96V furnaces

Two options exist for the condensate vent riser height. The choice decides whether the furnace keeps running when the drain is blocked.

1. Option A: put the top of the vent tube below the lower condensate water level sensor. The furnace keeps running when the drain is blocked, but water spills from the tube. Make sure there is a way to handle that water.
2. Option B: put the top of the vent tube above the lower condensate water level sensor. A blocked drain shuts the furnace down and no water spills.
3. Choose the option based on the customer's acceptance of overflow versus loss of heat.

Confirm the gas type matches the rating plate

Rheem · 96V and 96MDV series furnaces

Use the furnace only with the gas type approved for it. The furnace rating plate lists the approved gas.

1. Read the furnace rating plate.
2. Confirm the supply gas matches the approved type before firing the unit.

Evaporator coil airflow order and damper control

Rheem · Furnaces used with a cooling evaporator coil

With a cooling evaporator coil, air must pass over the heat exchanger before it passes over the cooling coil. Cold air over the heat exchanger tubes can cause internal condensation, corrosion and eventual failure. Manual dampers must be arranged so heating or cooling cannot run unless the damper is in the full heat or full cool position.

1. Confirm the airflow path goes through the heat exchanger before the cooling coil.
2. Confirm manual dampers block heating or cooling operation unless fully in the correct position.

Expose fresh copper on reused thermostat wire

Rheem · 96V and 96MDV communicating systems

Old wire from a previous installation must be prepared before connecting it, or the communication link may not establish.

1. Trim back the wire tip past the old insulation.
2. Strip a small amount of insulation to expose clean new copper for the communicating connections.

Gas pressure regulator and purging

Rheem · Gas supply pressure and purging

A regulator may be needed in the supply line. Its outlet must not exceed the maximum supply pressure on the rating plate. Industrial regulators are not allowed. Gas piping must be purged to a safe location per NFGC section 8.3.

1. Confirm the regulator will not deliver more than the maximum supply pressure on the rating plate.
2. Do not use an industrial-type gas regulator.
3. Purge the gas piping following local codes and NFGC section 8.3 so no explosive mixture can build up.
4. Only connect to gas from a commercial utility or commercial fuel provider.

Gas valve connection and leak check

Rheem · Gas valve and piping connections

Pipe strain can move the burner orifices and cause erratic operation. Leaks must be found with a soap solution, never an open flame.

1. Use a back-up wrench on the manifold and gas valve when making the connection so the valve does not twist.
2. Do not overtighten the gas valve onto the pipe.
3. Use a pipe compound that resists LP gas on all threaded joints.
4. Check all gas fittings with a soapy solution. Bubbles mean a leak to fix.
5. Never test for leaks with an open flame.

Ground thermostat wire shield at one point only

Rheem · 96V and 96MDV communicating systems

Shielded thermostat wire is used where the wiring runs near high voltage, cable TV, Ethernet or radio equipment. The shield must be continuous and grounded in only one place.

1. Twist shield wires together across each segment so the shield is continuous.
2. Connect the shield to the C terminal or ground at the indoor unit.
3. Do not connect the shield to any terminal at the thermostat.
4. Do not ground the shield at both ends.

Install only in an approved location and position

Rheem · 96V and 96MDV series furnaces

Place the furnace only in a location and position listed in the location requirements section. Any other placement can cause unsatisfactory operation or dangerous conditions and voids the warranty.

1. Check the location requirements section before setting the furnace.
2. Confirm the installation follows the CSA certification and these instructions.

Leak test gas connections with soap solution only

Rheem · 96V and 96MDV series furnaces

Never check for gas leaks with an open flame. Use a commercial leak-detection soap solution on all connections covered in the gas supply and piping section.

1. Apply leak-detection soap solution to every gas connection.
2. Look for bubbles and fix any leak before startup.

Legacy 1-stage thermostat jumper

Rheem · 96V and 96MDV furnaces with legacy thermostats

A legacy 1-stage thermostat with autostaging is wired to the furnace. For one-stage cooling a jumper is needed between Y1 and Y2.

1. Wire the legacy 1-stage thermostat per the autostaging wiring diagram.
2. Install a jumper between Y1 and Y2 for one-stage cooling.
3. The jumper is only used for heat pump installations in the wiring diagram.

Level the furnace with a slight tilt toward the front

Rheem · All orientations

Install the furnace level from front to back or with a slight tilt so the back is up to 1/2 inch higher than the front. Figure 3 gives the tilt as 1/4 inch minimum to 1/2 inch maximum toward the front in all installations and orientations.

1. Set the cabinet level or tilted 1/4 in. to 1/2 in. toward the front.
2. Verify the tilt in upflow, downflow and horizontal orientations.

Limit total static pressure on the distribution system

Rheem · All 96V and 96MDV series furnaces

Total static pressure drop of the whole air distribution system, including any AC coil, air filtration, zoning, and ductwork, must not exceed 0.8 in W.C. Size the duct for the maximum possible airflow, because heating airflow can be higher than cooling airflow. Check the added equipment data for pressure drop at the recommended heating or cooling CFM.

1. Size duct to the maximum airflow value, not just the cooling value.
2. Add up pressure drop of coil, filters, zoning and ductwork.
3. Confirm the total is 0.8 in W.C. or less at recommended CFM.

Massachusetts CO detector and signage rules for sidewall horizontal venting

Rheem · Sidewall horizontal vent installations in Massachusetts

In Massachusetts, sidewall horizontally vented gas equipment with the exhaust termination less than 7 feet above finished grade (including over decks and porches) needs hard-wired CO detectors with battery backup on the floor where the appliance is installed, plus CO detectors on each additional level. A metal or plastic sign reading GAS VENT DIRECTLY BELOW. KEEP CLEAR OF ALL OBSTRUCTIONS must be mounted 8 feet above grade in line with the vent. Detectors must meet NFPA 720 and ANSI/UL 2034 and be IAS certified. If the detectors cannot be installed at completion, a battery CO detector must be used during the 30-day allowance.

1. Confirm the exhaust termination height above finished grade.
2. Install hard-wired CO detectors with battery backup on the appliance floor and on each additional level.
3. If not possible at completion, install battery CO detectors and finish the hard-wired installation within 30 days.
4. Mount the required warning sign 8 feet above grade in line with the exhaust terminal.

Non-communicating condenser wiring

Rheem · 96V and 96MDV communicating furnaces with non-communicating condensers

A non-communicating condenser or heat pump used with a communicating furnace and thermostat needs a special configuration.

1. Run four dedicated wires (E1, E2, R and C) from the furnace to the condenser.
2. Use a daisy-chain layout only; a star layout is not approved.
3. Wire the thermostat using the non-communicating condenser diagram.

Preparing the furnace for installation

Rheem · 96V and 96MDV series furnaces

Remove the solid metal base pan from the top of the furnace. It is for shipping only and must not stay in place after installation. Install the furnace with a 1/4 inch to 1/2 inch forward slope toward the front for drainage. Allow access for service.

1. Remove the solid metal base pan from the top of the furnace.
2. Set the furnace with a 1/4 inch to 1/2 inch forward slope toward the front.
3. Leave room for service access.

Protect the condensate trap and line from freezing

Rheem · Condensate trap and condensate lines

If the furnace sits where temperatures can drop below freezing, the trap and condensate line will freeze. That shuts the furnace down or damages the trap unless freeze protection is installed.

1. Install freeze protection on the trap and all condensate lines wherever freezing is possible.
2. Do not run the condensate drain outdoors. Frozen condensate can cause property damage.

Receiving and pre-install checks

Rheem · 96V and 96MDV series furnaces

Inspect all cartons on arrival and note any transit damage on the delivery papers before filing a claim. Verify the carton and rating plate model numbers match the job before opening the carton. Check the rating plate against job specs.

1. Inspect cartons immediately for transit damage and note it on the delivery papers.
2. Compare the carton label model number with the job order before opening.
3. Open the carton and confirm the furnace rating label matches the carton model number.
4. Check the rating plate matches the job specifications.
5. Read the full instructions before starting.

Replace furnaces immersed in water

Rheem · 96V and 96MDV series furnaces

Any equipment immersed in water, including by flooding, must be replaced. Water-damaged equipment will have its operation adversely affected and the warranty is void.

1. Replace any furnace that has been immersed in water, including by flooding.

Replacing the furnace control: keep the memory card and copy the dipswitches

Rheem · (-)96VA040-115 (R96V / U96V) and (-)(-)96MDV040-115 two-stage variable-speed communicating furnaces

The model data lives on a memory card tethered to the furnace; the new control is useless without it.

1. Pull the memory card out of the old control and plug it into P6 of the replacement. Do not cut the plastic tether.
2. Copy every dipswitch position from the old board to the new one.
3. Never use a control or card from another furnace, condenser or air handler. A lost card is ordered from ProStock by furnace model and serial number; cycle power after fitting it or the data is not read.

Return air and outside air limits

Rheem · All 96V and 96MDV series furnaces

When outside air is used, the system must hold return air above 55 F during the heating season. Return grilles and warm air registers must not be blocked or closed. Do not take return air from furnace rooms, garages, cold areas, utility rooms, kitchens, laundry rooms or bathrooms.

1. Check return air temperature stays above 55 F with outside air in use.
2. Confirm return grilles and warm air registers are open.
3. Route return air from an approved area only.

Review checklist after horizontal right conversion

Rheem · Horizontal right conversions (96V and 96MDV)

Check these items before you leave the job after the horizontal right conversion.

1. Make sure all hoses are secure and fully seated.
2. Check that no hose has kinks.
3. Confirm all hoses and drain parts slope in the direction of water flow.
4. Confirm both worm-drive clamps on the flue transition are tight.
5. Tighten all clamps and couplings.
6. Plug all drain ports.
7. Confirm the unit has forward pitch.
8. Install heat tape if the site requires it.
9. The drain trap must sit on top of the coupling, per the location detail in the general conversion instructions.

Set input rate and temperature rise to the rating plate

Rheem · 96V and 96MDV series furnaces

The furnace must run within its intended temperature-rise range on a duct system with external static pressure in the allowable range. Set input rate and temperature rise to the rating plate markings. Return air temperature must stay between 55°F (13°C) and 80°F (27°C).

1. Check external static pressure against the ducting section limits.
2. Set the input rate and temperature rise per the rating plate.
3. Keep return air between 55°F (13°C) and 80°F (27°C).
4. Verify ignition, input rate, temperature rise and venting after the job is complete.

Single-stage thermostat on a two-stage furnace: auto staging

Rheem · (-)96VA040-115 (R96V / U96V) and (-)(-)96MDV040-115 two-stage variable-speed communicating furnaces

With only W1 wired, the furnace can step itself up to high fire after a set time.

1. Set S2-10 / S2-11: OFF-OFF normal two-stage (default); ON-OFF 10 min on low then high; OFF-ON 15 min; ON-ON 20 min.
2. A W2 call still forces high stage even with auto staging on.
3. Communicating systems ignore the dipswitches; staging is set at the thermostat.

Site selection and service clearance

Rheem · All installations

Choose a site near the center of the duct system, keep vent runs short with minimal elbows, and locate the furnace near existing gas piping. Keep at least 24 in. (30 cm) of service clearance in front of all furnaces. Use the 24 in. figure if accessibility clearance is greater than the fire protection clearance.

1. Place the furnace near the center of the duct system.
2. Keep the vent run short with minimal elbows.
3. Keep at least 24 in. (30 cm) in front of the furnace for service.

Test a new safety switch before handing over

Rheem · 96V and 96MDV series furnaces

A newly installed safety switch must be tested under load with the blower and burner door in place. If the closet door is part of the installation, it must be closed during the test. Multi-stage furnaces need a second test at minimum input.

1. Install the blower and burner door.
2. Run the furnace at maximum input rate for at least 15 minutes.
3. If the closet has a door, keep it closed during the test.
4. On a multi-stage furnace, repeat the test at minimum input rate.

Thermostat setpoint for startup tests

Rheem · 96V and 96MDV furnaces

High stage is only called when the thermostat setpoint is more than about 2 F above room temperature. Low stage is generally called with the setpoint about 1 F above room temperature. Confirm with the thermostat specs.

1. Set the thermostat setpoint for high stage and verify high heat for 15 minutes.
2. Set the thermostat setpoint for low stage and verify low heat for 15 minutes.

Wire auxiliary switches to T5

Rheem · 96V and 96MDV communicating systems

Up to two field switches (drain pan, smoke detector, freeze switch and similar) can be wired to the T5 auxiliary inputs on communicating systems only.

1. Wire each switch to Aux 1 or Aux 2 on terminal T5.
2. At the communicating thermostat, set each input as normally open or normally closed.
3. Configure what the system does when the contacts open or close at the thermostat.

Do not light burners manually

Trane · Furnace startup

The control handles ignition automatically.

1. Turn on the main electrical supply and set the thermostat above setpoint.
2. The ignitor heats first, then the gas valve opens.
3. After flame is proven, the flame control keeps the gas valve open until the thermostat is satisfied.
4. Run the unit through one complete cycle at startup.

Downflow installation on combustible floors

Trane · Downflow furnaces

Do not set the furnace directly on carpet, tile or other combustible material except wood flooring.

1. For a vertical downflow installation, use subbase BAYBASE-205 between the furnace and combustible flooring.
2. A subbase is not required when a downflow furnace is installed vertically with a cased coil.