Complete Wiring Guide for Aprilaire Model 60 Humidifier

The 60 series control system requires precise connections to function correctly. Begin by locating the 24V transformer terminals–these are typically marked R (power) and C (common). Connect the humidistat’s power wire (often red) to the R terminal and the common wire (usually white or blue) to the C terminal. This establishes the baseline circuit needed for operation.

Next, identify the solenoid valve wires. These carry low-voltage signals to activate water flow. Attach the humidistat output (commonly a green or yellow wire) to the valve’s positive terminal. The negative terminal should link back to the transformer’s C terminal. Verify all connections with a multimeter–readings should show 24V AC when the system calls for humidity.

Avoid common pitfalls: Do not mix line-voltage and low-voltage wires, as this can damage components. Ensure the water supply solenoid is properly grounded–use a 18-gauge stranded copper wire connected to a grounded junction box. If the system includes a drain pump, wire it in parallel with the solenoid but confirm voltage compatibility (some pumps require 120V).

For troubleshooting, check the fuse on the control board–replace it if blown. If the unit fails to power on, trace the circuit from the transformer to the humidistat and valve, testing each junction for continuity. Always disconnect power before inspecting or modifying connections to prevent short circuits or electrical hazards.

Electrical Hookup Guide for the 60-Series Humidifier

Identify the transformer terminals first–common markings include R (24V hot), C (common), and W (humidistat connection). Connect the red wire from the humidifier’s solenoid to R and the white wire to W. Ensure the transformer supplies 24V AC; verify with a multimeter before securing connections to avoid voltage mismatch.

• For standalone units, use a dedicated 24V transformer with at least 40 VA capacity.
• If integrating with a furnace, splice into existing R and C terminals using 18-gauge wire.
• Avoid combining with high-load circuits like blower motors to prevent voltage drop.

The humidistat requires proper placement–mount it on the supply plenum downstream of the heating coil. Drill a 3/8″ hole, insert the sensing element, and seal with the provided gasket. Misplacement leads to erratic operation. For bypass configurations, ensure the drain tube slopes at least 1/4″ per foot to prevent water buildup.

For series 60 units with optional outdoor temperature sensors, wire the sensor in parallel with the humidistat’s W terminal. The sensor overrides the humidistat at temperatures below 20°F to prevent frost formation. Use exterior-grade wire for outdoor runs to resist moisture ingress.

Test the setup by setting the humidistat to 35% RH and verifying water flow. If the solenoid clicks but no water appears, check for:

1. Clogged orifice–clean with vinegar or compressed air.
2. Low water pressure–minimum 15 PSI required.
3. Faulty solenoid–measure 24V across terminals; replace if no voltage.

Follow NEC Article 424 for humidifier circuit protection. Use a 20A breaker for dedicated transformers or a 15A breaker if sharing with furnace controls. Label all connections with heat-shrink tubing for future maintenance. Store spare parts (solenoid, orifice, saddle valve) onsite to minimize downtime.

Step-by-Step Guide to Identifying Terminal Connections on the Ventilation Unit

Locate the control board on the right side of the unit, typically enclosed behind a removable cover. Remove the cover by unscrewing the two Phillips-head fasteners. The terminals are labeled R, C, W, G, and Y–align these markings with the standard 24V HVAC color-coding: R (red), C (blue or black), W (white), G (green), and Y (yellow). Verify each terminal’s voltage using a multimeter set to AC mode; R to C should read 24-28V, while the others should drop to near 0V when inactive.

• For humidistat-controlled installations, identify the auxiliary terminal labeled H or Hum. Connect the humidistat’s H wire here–typically brown or purple–ensuring it’s secured with a terminal screw tightened to 8-10 in-lbs.
• If integrating with a heat pump, trace the O/B terminal (often orange) and confirm its absence on this unit; substitute by splicing into the Y circuit at the thermostat or air handler instead.
• Label all wires at both ends before disconnecting any connections to prevent mispairing. Use 18-22 AWG solid copper wire for all low-voltage links, stripping only 3/8″ of insulation for a secure fit under terminal screws.

Common Installation Errors and Diagnostic Steps

Reverse polarity on terminals R and W causes the unit to power on but fail to engage heating. Use a multimeter to verify R carries 24VAC relative to C; W should show 0V until the thermostat calls for heat. Swap wires if readings are inverted.

Loose connections at the control board create intermittent faults or false E5 errors. Tighten screws with a torque screwdriver set to 0.5 Nm–over-tightening cracks terminal blocks. Re-check continuity with the meter before securing the cover.

Mixing low-voltage and line-voltage conductors triggers immediate short circuits. Keep 120V inputs isolated from 24V outputs by routing them in separate conduits. Label each wire at both ends with heat-shrink tubing for future reference.

Skipping the humidistat jumper on a two-stage system forces continuous operation. Confirm the jumper between HUM and HUM2 terminals is intact; if removed, reinstall a 0.5 mm² solid copper bridge. Verify operation by monitoring the display for mode changes.

Misaligned sensor leads cause erratic humidity readings. Ensure the yellow and green wires are firmly seated in the Molex connector–push until an audible click confirms lock. Replace the sensor if readings fluctuate more than ±2% RH over 30 minutes at stable ambient conditions.

Fault Code	Symptom	Test Point	Expected Value
E1	No power to solenoid	Between R and C	24VAC ±1V
E2	Short on HUM circuit	Between HUM and C	<1V
E3	Sensor open	Sensor resistance	10 kΩ ±5% at 25°C

Grounding the 24V neutral to the chassis distorts sensor readings. Separate the neutral wire from any metal mounting points by at least 6 mm. Use a non-contact voltage tester to confirm zero potential between neutral and ground before energizing the unit.

Damaged thermostat cable prevents communication between stages. Replace any cable showing nicked insulation or exposed strands; use solid-core 0.8 mm² wire for runs over 15 m to prevent voltage drop. Test continuity end-to-end with a resistance setting on the meter–values above 2 Ω indicate breakage.

Integrating the Humidifier 60 with a 24V Control System: Precise Connection Steps

Identify the humidifier’s R and W terminals–marked on the device’s internal control board. Connect the R terminal to the thermostat’s 24V Rh or Rc wire (red, standard for power). Link the W terminal to the thermostat’s W output (white, activates during heating demand). Verify voltage with a multimeter: 24V AC between R and C (common) confirms power; W should show 24V only when calling for humidity. Use 18-gauge solid copper wire for all connections, securing with wire nuts or clamp terminals to prevent vibration loosening. If the system includes a furnace with a separate humidifier terminal, bypass it–connect directly to the thermostat for consistent control.

Solenoid and Transformer Configuration

Locate the solenoid valve (brass component on the water supply line) and ensure its coil wires match the humidifier’s W terminal. Split the 24V circuit: one leg powers the humidifier’s solenoid (via W), while the second supplies the onboard control (via R). For transformers under 40VA, add a dedicated 24V AC transformer (Class 2, NEC-compliant) to avoid overloading the thermostat or furnace circuitry. Mount the transformer near the humidifier, using a fused disconnect (3A) for safety. Test operation by setting the thermostat to “heat” and adjusting the humidifier dial–audible solenoid clicks and water flow should start within 5 seconds.

Essential Gear and Supplies for Installing Your Humidification Unit

Begin with a multimeter calibrated for 200V AC range–non-negotiable for verifying transformer output at the solenoid valve before connecting power. Autoranging models risk masking voltage drops that could damage control circuits over time.

Wire strippers with 18-22 AWG notches prevent nicking conductors; thermal strippers avoid insulation melt but require steady hand pressure to prevent scoring. For stubborn terminals, crimp connectors must match the wire gauge–fork-style for screw-down connections, butt-style for inline splices.

Precision screwdrivers with magnetized tips hold #8 and #10 screws during panel removal; Phillips #2 for motor housings, flathead 3/16″ for duct dampers. Avoid power drivers–torque settings above 12 in-lbs risk stripping screw heads on plastic mounting brackets.

Fish tape (non-conductive fiberglass) guides cables through tight ductwork bends without damaging foil insulation. Lubricate with silicone spray before threading; petroleum-based lubricants degrade PVC conduit over time.

Heat-shrink tubing (3:1 ratio) seals connections against condensation–polyolefin for standard runs, dual-wall adhesive-lined for outdoor vents. A 120W heat gun with variable temperature (300°F minimum) prevents overheating delicate sensor wires.

Cable ties must be UV-stable nylon (6.6 tensile strength) for outdoor installations; mount every 6 inches along rigid ducts to prevent vibration-induced wear. Stainless steel ties resist corrosion near evaporator coils but require side-cutting pliers for clean trimming.

Insulated quick-disconnect terminals (blue for solenoid, red for transformer) simplify future maintenance–avoid soldered connections inside furnace cabinets due to heat cycling. Dielectric grease applied sparingly to terminals prevents oxidation without impeding conductivity.

Grounding straps (braided copper, 12 AWG) bond all metal components within 4 feet of the unit–verify continuity with a megohmmeter before energizing. For final checks, a non-contact voltage tester confirms de-energization before handling live circuits.