UNIT TROUBLESHOOTING (cont)

PROBLEM

POSSIBLE CAUSE

 

CORRECTIVE ACTION

 

No fan status

Check status of SFS (4 STAT). If supply fan status switch is

 

OFF, check switch for proper operation.

 

 

 

Mixed-air dampers forced closed to outside air

Check status of MIXD (5 STAT). If MIXD is forced, remove

 

force and check operation.

 

 

 

 

Check for blown fuse (F7). Replace if necessary. If fuse is

 

No power to damper actuator

intact, check for proper connections. Check transformer

Mixed-air dampers

 

output.

will not operate

Incorrect reading from space temperature sensor

Check status of sensor readings for accuracy. Replace sen-

 

or supply-air temperature sensor

sors if defective.

 

 

Check con®guration for proper SMG and MDP (minimum

 

 

damper position). If MDP is set to zero, then dampers will

 

Con®guration error

stay closed when enthalpy is unsuitable. An improper SMG

 

can cause the MIXD to be held to the MDP setting. Check

 

 

 

 

for proper damper set point. If damper set point is forced to

 

 

incorrect value, remove force.

 

No fan status

Check status of SFS (4 STAT). If SFS is OFF, check supply

 

fan status switch for proper operation.

 

 

 

Inlet guide vanes (IGVs) forced closed

Check status of IGV (5 STAT). If IGVs are forced, remove

 

force and check operation.

 

 

 

 

Check for blown fuse (F4). Replace if necessary. If fuse is

Unit not main-

No power to IGV actuator(s)

intact, check for proper connections. Check transformer for

taining desired

 

proper output.

static pressure

Loose IGV linkage

Check IGV linkage for tightness and proper adjustment.

(VAV units only)

 

 

 

 

Check status of sensor reading for accuracy. If reading is

 

 

 

Incorrect reading from static pressure transducer

in error, check for plugged sensing line and check sensor

 

 

calibration. Replace sensor if defective.

 

 

Check con®guration for proper static pressure set point.

 

Con®guration error

Also, check SMG. An improper SMG can cause the IGVs to

 

 

be held closed.

 

IGVs forced open

Check status of IGV (5 STAT). If IGVs are forced, remove

 

force and check operation.

 

 

 

High-Pressure Switch (HPS) is incorrectly set

Using squeeze bulb, check trip point of HPS. Adjust as re-

High-Pressure

or defective

quired. Check for plugged lines. Replace if defective.

Switch keeps

 

Using local interface device and squeeze bulb with gage,

tripping unit

Static pressure sensor reads incorrectly

verify static pressure reading is correct. Adjust or replace

OFF (VAV only)

 

sensor as required.

 

 

Check con®guration for proper static pressure set point.

 

Con®guration error

Check SMG. An improper SMG can cause the IGVs to be

 

 

held open.

 

 

Check fuses of speci®c actuator for function failure.

 

 

Fuses are as follows:

 

 

F1 Ð PSIO control module

 

 

F2

Ð Power

 

 

F3

Ð Cooling coil

 

 

F4 Ð IGVs Ð supply fan

 

 

F5 Ð DSIO or option module

 

No power, blown fuse

F6

Ð Heating coil

 

 

F7 Ð Mixed-air dampers

Individual

 

F8 Ð Smoke control or return-air damper

 

F9 Ð Exhaust-air damper

actuators

 

 

F10 Ð IGVs Ð return fan

do not function

 

 

F11 Ð 39NX sizes 74, 92; 2nd IGV actuator, supply fan

 

 

 

 

F12 Ð 39NX sizes 74, 92; 2nd IGV actuator, return fan

 

 

F13 Ð Preheat coil

 

Linkage is jammed or binding

Using manufacturer's instructions, correct and adjust

 

linkage. Check operation.

 

 

 

 

Using Quick Test and a voltage meter set to measure cur-

 

No control signal

rent, verify that the proper control signal (4 to 20 mA) is be-

 

ing sent to the actuator. Refer to wiring diagram for

 

 

 

 

appropriate terminals.

Oscillating

Incorrect submaster gain

Using Control Loop Checkout procedure, page 108, adjust

the SMG until the output steadies.

output

 

 

Verify sensor reading. If reading is ¯uctuating, determine

(HCV, CCV, IGV,

Input sensor is ¯uctuating (supply-air

cause (i.e., loose connections, partially plugged static pres-

MIXD, etc.)

temperature sensor, static pressure transducer)

sure sensing lines). Correct or replace sensor if necessary.

 

 

 

Loose connections

Verify all connections are secure.

 

 

Voltage type sensors (i.e., static pressure, space tempera-

Sensor

Sensor out of calibration

ture, outdoor-air temperature, return-air temperature, rela-

tive humidity, and velocity pressure) can be calibrated using

not reading

 

 

manufacturer's instructions.

correctly

 

 

If a sensor cannot be calibrated and its reading is consid-

 

 

 

Defective sensor

ered unacceptable, replace sensor. Once sensor is re-

 

 

placed, verify new sensor is reading correctly.

114

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Image 114
Carrier 39L specifications Hcv, Ccv, Igv

39L specifications

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