Have you ever wanted a simplified explanation???

Buckle up... This is as simple as it gets

This article's intent is to demystify the confusion around: 

• Terminals
• Low Voltage
• Jumpers
• Terminology

Terminals

Low Voltage

I find that most of the confusion surrounds the higher SEER rated equipment and the operation of the "Y2out", "Wout", "W1out" and "W2out". I will focus most of the explanation around the operation of these terminals and higher SEER systems.

Because of the technology inside many of these higher SEER and Variable Capacity condensers, they have been given the ability to control the staging and fan speeds INSTEAD of the thermostats, furnaces and air handlers. This allows many thermostats and furnaces to be installed on a wide variety of system applications with the ability to maintain very close room temperature set points.

That being said....

High SEER - Air Conditioners

• The "Y2" signals that come from the thermostats, will always go to the condenser section first.
• The condenser will then determine the load on the system and provide a "Y2out" signal inside to the furnace's "Y2" or air handler's "Y2" (or fan motor directly) as a input to increase the fan speed.

High SEER/HSPF - Heat Pumps

• The "W", "W2", "E", "Aux" signals that come from the thermostats, will always go to the heat pump section first.
• The heat pump will then determine the load and defrost timing for the system and provide a "W1out" signal inside to the furnace's "W1" or air handler's "W1" as an input.
• If the heat pump determines it needs to upstage, it will send a signal on "W2out" to the furnace's "W2" or air handler's "W2". (15 minute delay for W2out signal)
• If it has multiple stages of gas heat or electric elements, and only a ONE stage heat pump, then "W1' and "W2" will have to be jumpered at the furnace to let the board time-on stage 2 (or a delay-on-make timer may be used between "W1" and "W2" on an A/H)
• Never jumper "W1out" and "W2out" together because of back feeding
• Cap any unused wires with a wire nut
• If the thermostat is put into the Aux or Emergency position, the heat pump will NOT energize the compressor and instead energize the "Wout" signal back to the furnace or A/H (and stage-on W2out if applicable)

AVC Air Handler and TH4B Heat Pump Example

Jumper Positions

ATR Jumper - 3 Positions Available

• The ATR is the only temp rise adjustment available for modulating furnaces
  • +10 degree rise - LOWERS CFM - (40-65ºF)
  • Normal - NO adjustment to CFM - (40-55ºF)
  • -10 degree rise - INCREASES CFM - (40-45ºF)

Cooling Speed Jumper - 4 Positions available

• The airflow delivered by the furnace during compressor operation can be adjusted to match the capacity of the compressor section. This is a base CFM that can be fine-tuned with the Adjust Jumper. 
• Follow the CFM chart in manual associated with your specific compressor tonage

Adjust Jumper - 3 Positions available 

• The ADJ jumper has three positions which can be used to make further adjustments to the cooling blower airflow.
• Follow the CFM chart in manual associated with your specific compressor tonage

Continuous Fan Speed Jumper - 3 Positions available

• The airflow delivered by the furnace during continuous fan operation
  • L - 40% of max blower speed 
  • M - 70% of max blower speed
  • H - 100% of max blower speed
  • If jumper is left off the system will default to H (100%)

Delay Jumper - 4 Positions available

• The set of jumper pins on the control board labeled “DELAY” are used to set the fan delay (ramping) profiles for the furnace blower. These can be chosen so as to maximize the comfort and sound levels for various regions of the country

A - Default

B - Humid:

C - Dry:

D - Temperate:

Hum Stat Jumper

• The HUM STAT jumper configures the control to monitor the humidity
  switch input. With the jumper in the NO position, the control will ignore
  the HUM input. With the jumper in the YES position, the control will
  monitor the HUM input to control the blower speed for de-humidification
  during cooling operation.
• If the jumper is not present, the control will operate as if the jumper is in
  the NO position.

AC/HP Jumper

• The AC/HP jumper configures the control to operate properly with an air
  conditioner (AC position) or heat pump (HP position).
  • With the jumper in the AC position, the control will treat any “Y” call as a cooling call.
  • With the jumper in the HP position, the O input signal is received from the
    room thermostat. This allows the control to recognize whether it is in the
    heating or cooling mode and energizes the 24 VAC HUM output when
    blower is on and a first stage heating call is present.
• If the jumper is not present, the control will operate as if the jumper is in the HP position.

Zoning Jumper

• When zoned systems are installed, putting the ZONE CONTROL jumper on the furnace control board in the “YES” position will change the heating load logic to a special algorithm for multi-zone homes.
  • This algorithm operates at the “low demand” firing rate for 10 minutes and then ramps to high fire within 20 minutes (30 minutes maximum to get to 100% firing rate).
  • The special zoning algorithm does not have the Run 2 function, so the burners will stop firing as soon as there is no call for heating.

Terminology

Demand Response (Load Shedding)

• The outdoor control has a conventional 24VAC input (DR) for utility demand response signals. When a 24VAC signal is present on the DR input with a communicating system, the HX™ thermostat will adjust the indoor temperature setpoint by the installer selected setting.
• With a non-communicating system, a 24VAC signal on the DR terminal will not allow the system to run in second stage, cooling operation only.

Y2LOCK

• Moving the Y2 LOCK jumper to ON enables the two-stage cooling anticipation feature. Two-stage cooling anticipation forces the system to start at full capacity, by-passing first stage operation if there are two consecutive calls for second stage operation. On the next call for 1st stage cooling, the control forces 2nd stage operation. The control logic assumes that if the last two cooling calls required full capacity, the next cooling call will likely require full capacity.  The space temperature does not have to increase to 2nd stage before full capacity is engaged.
  • • Forced second stage anticipation remains active until:
      1. 1. The first stage cooling cycle from the thermostat becomes <10 minutes
         2. 24VAC to the control is cycled
         3. The outdoor control push button is depressed

• If Y2 LOCK is in the ON position, the control will stay in second stage until the thermostat is completely satisfied (Finish on High Stage - No Down Staging). Therefore a "Y2Out" signal will be needed from the outdoor section back to the indoor section in order to keep the fan running at the Y2 CFM setting even if the thermostat down stages to Y1
• If Y2 LOCK is in the OFF position, the control will allow the unit to switch from second stage back to first stage according to the room thermostat call.

Hot Heat Pump

• If the compressor is in 3rd stage and the hot heat pump jumper is in the ON position, the control can not output 24 VAC on “Y2out” in order to run with the Reduced Airflow Feature
  • The “Y2out” signal must also be connected to the indoor unit for this feature to function properly.
  • The Reduced Airflow Feature creates the Hot Heat Pump by controlling the indoor airflow level during heating operation only. The cooling operation is not affected. The control changes the indoor airflow level using the “Y2out” signal terminal. The “Y2out” terminal connects to the high speed cooling input of a variable speed indoor unit. When the heat pump control energizes the “Y2out” terminal, the indoor blower runs at high speed delivering high airflow and therefore lowering the leaving air temperature.
  • When the control de-energizes the “Y2out” terminal, the indoor airflow level reduces as the blower runs at a lower speed delivering lower airflow and a higher leaving air temperature.
• If the compressor is in 3rd stage and the hot heat pump jumper is in the OFF position, the control outputs 24 VAC on “Y2out.”

Run 2 - Minimizes temperature swings between cycles

• The board logic instead of the thermostat determines the CPH (Cycles Per Hours) with Run 2 
• When the equipment operates independent of a thermostat call, it's called a Run 2 cycle

Cooling Run 2

With the use of a 1 stage thermostat and a 2 stage AC condenser, the board logic determines when to bring on the 2nd stage of compressor and indoor fan speed. Here's what's happening in the logic...

Heating Run 2

Following the completion of the traditional heating cycle, the modulating gas furnace may continue to fire for a predetermined period of time to maintain close tolerance to the desired thermostat setpoint. Here's what's happening in the logic...