Carrier ZONECC3Z instruction manual LAT Limit, Error Codes, Automatic Checkout, Bypass Adjustment

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Dipswitch 7 and 8 - Sets LAT limit temperature. See LAT Limit Selection for proper setting. Default is OFF = 145° limit.

The following dipswitches are on the HP/2S control only: Dipswitch 9 - Informs the control whether it is connected to a heat pump or an air conditioner. OFF selects HP. ON selects AC. Default is OFF (HP).

Dipswitch 10 - Informs the control of the type of thermostat being used. OFF selects HP thermostat. ON selects AC thermostat. A HP thermostat may not be selected if the system selection is AC. A 2-stage heat AC thermostat or a HP thermostat may be used with a single stage HP. Default is OFF.

Dipswitch 11 - Disables LAT and HPT safeties when ON. ON is intended only for emergencies. When ON is selected, there is no over/under temperature protection for the equipment. Default is OFF.

Dipswitch 12 - Informs the control whether the reversing valve is energized in cooling (O function) or heating (B function). ON selects B function. OFF selects O function. Default is OFF.

LAT Limit Selection

To accommodate varying heat rises in furnaces and fan coils, the LAT limit adjustment has four selections: 130, 145, 160 and 175 degrees. In addition to these, the HPT limit is fixed at 115 degrees and the cooling limit (also sensed by LAT sensor) is 40 degrees. To select the proper limit, check or calculate the rated maximum rise of the equipment. Add 75 degrees to this value. Pick the closest LAT limit choice below this value and use dipswitches 7 and 8 to enter this value using:

Table 5—LAT Limit

TEMPERATURE	SWITCH 7	SWITCH 8
130	OFF	ON
145 (default)	OFF	OFF
160	ON	OFF
175	ON	ON

Take a minute to study the LAT Limit table. Note that the limits are the final shutdown temperatures, but actions begin earlier. First, at levels 1 and 2, closed dampers begin to open gradually, followed at level 3 by staging down of multi stage equipment, if it exists. Under most limit challenges, the system will stabilize between 1 and 3 due to opening of closed dampers.

UNIT DAMAGE HAZARD

Failure to follow this caution may result in unit damage. Setting LAT limit too high can shorten the life of the HVAC equipment.

Automatic Checkout

An automatic checkout procedure is provided which will exercise dampers, heating, and cooling in that order. It is described under the Understanding System Operation section in Installer Test Mode. This may be used or the system may be checked out manually by creating thermostat calls. When using thermostats, remember that only the calling zoning dampers will be open. This provides the means to select which dampers are open for any heating or cooling call. It is advisable that the initial checkout be made with all dampers open before the bypass is set. This can be done by temporarily setting Switch 5 to ON (disable zoning) and controlling the equipment from the Zone 1 thermostat. When the equipment is operating satisfactorily, return Switch 5 to OFF and proceed to the next section.

Bypass Adjustment

The bypass should be set to the highest possible pressure setting consistent with an acceptable air noise level. To set, operate the system with a call from the smallest zone at its highest airflow (highest may be either heating or cooling). This condition forces the largest amount of air through the smallest duct, creating the highest static pressure at the bypass. Adjust the bypass pressure setting so that the bypass stays closed. Then check to determine if the level of noise and ″blow″ in that zone is acceptable. If it is unacceptable, reduce the bypass pressure setting (see bypass instructions for how to adjust) until it just begins to crack open. Check again, continuing the process until an acceptable noise and ″blow″ level is reached.

If, under this condition, the LAT approaches its limit, the system will open the other closed dampers until the LAT reaches an acceptable level. This operation is acceptable. The system will automatically open dampers enough to keep the LAT at a safe value, and will do it only when the zone demands require it. You may observe the limit level on the status LED (if it is above zero). If it stabilizes at a value of higher than 2, an overly small duct system is indicated and it would be desirable to raise the bypass pressure setting, if possible.

Error Codes

The status LED indicates normal operation, problems, and LAT/HPT limit status according to a two digit code. The first digit flashes its number, followed by a 2 second pause, followed by the second digit, followed by a 4 second pause. The cycle the repeats. The codes are:

Table 6—Error Codes

ON CONTINUOUSLY	NO PROBLEMS
11 - 17	LAT limit level 1 - 7
21 - 27	HPT limit level 1 - 7
31	LAT shorted
32	LAT open
33	HPT open
34	HPT shorted
41	Invalid: Sw 9=ON; Sw 10=OFF

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