Carrier 48/50Z030-105

DIAGNOSTIC ALARM CODES AND POSSIBLE

CAUSES

T051 (Circuit A, Compressor 1 Failure)

T052 (Circuit A, Compressor 2 Failure)

T055 (Circuit B, Compressor 1 Failure)

T056 (Circuit B, Compressor 2 Failure)

NOTE: These alerts only occur on units with a current sensor

board (CSB) (48/50Z105 only).

If the current sensor board reads OFF while the compressor

relay has been commanded ON for a period of 4 continuous

seconds, an alert is generated.

Any time this alert occurs, a strike will be called out on the

affected compressor. If three successive strikes occur the com-

pressor will be locked out requiring a manual reset or power re-

set of the circuit board. The clearing of strikes during compres-

sor operation is a combination of 3 complete cycles or 15 con-

tinuous minutes of run time operation. So, if there are one or

two strikes on the compressor and three short cycles (ON-

OFF,ON-OFF, ON-OFF) occur in less than 15 minutes, the

strikes will be reset to zero for the affected compressor. Also, if

the compressor turns on and runs for 15 minutes straight with

no compressor failure, the compressor's strikes are cleared as

well.

NOTE: Until the compressor is locked out, for the first two

strikes, the alert will not be broadcast to the network, nor will

the alarm relay be closed.

The possible causes are:

• High-pressure switch (HPS) open. The high-pressure switch

is wired in series with the compressor relays off of the

MBB. If the high-pressure switch opens while the MBB is

commanding the compressor on, the compressor stops and

the CSB no longer detects current, causing the control to

activate the alert.

• Circuit breaker trip.

• Wiring error.

To check out alerts T051, T052, T055, T056:

1. Turn on the compressor in question using Service Test

mode. If the compressor does not start, then most likely

the problem is one of the following: HPS open, circuit

breaker trip, incorrect safety wiring, or incorrect com-

pressor wiring.

2. If the compressor starts, verify that the indoor and

outdoor fans are operating properly.

3. If the CSB is always detecting current, then verify that the

compressor is on. If the compressor is on, check the

contactor and the relay on the MBB. If the compressor is

off and there is no current, verify CSB wiring and replace

if necessary.

4. Return to Normal mode and observe compressor opera-

tion to verify that compressor current sensor is working

and condenser fans are energized after compressor starts.

A051 (Circuit A, Compressor 1 Stuck On Failure)

A052 (Circuit A, Compressor 2 Stuck On Failure)

A055 (Circuit B, Compressor 1 Stuck On Failure)

A056 (Circuit B, Compressor 2 Stuck On Failure)

NOTE: These alarms only occur on units with a current sensor

board (CSB) (48/50Z105 only).

If the current sensor board reads ON while the compressor

relay has been commanded OFF for a period of 4 continuous

seconds, an alarm is generated. These alarms are only moni-

tored for a period of 10 seconds after the compressor relay has

been commanded OFF. This is done to facilitate a service tech-

nician forcing a relay to test a compressor.

In addition, if a compressor stuck failure occurs and the cur-

rent sensor board reports the compressor and the request off,

certain diagnostics will take place.

1. As A1 and B1 both have 1 unloader, the control will ener-

gize the particular unloader for these compressors if the

failure occurs.

2. If any of the 4 compressors are diagnosed as stuck on and

the current sensor board is on and the request is off, the

control will request the supply fan which will automati-

cally start building air flow control.

3. Heating will be disabled while any one of the compres-

sors has this problem.

The reset method will be manual for these alarms.

The possible causes are:

• Welded contact on compressor relay or contactor.

• Frozen compressor relay on MBB.

To check out alerts A051, A052, A055, A056:

1. Place the unit in Service Test mode. All compressors

should be Off.

2. Verify that there is not 24v at the contactor coil. If there is

24v at the contactor, check relay on MBB and wiring.

3. Check for welded contactor.

4. Verify CSB wiring.

5. Return to Normal mode and observe compressor opera-

tion to verify that compressor current sensor is working

and condenser fans are energized after compressor starts.

T057 (Circuit A, High Pressure Switch Failure)

T058 (Circuit B, High Pressure Switch Failure) — These

alerts occur on all units except the 48/50Z105 units (current

sensor board units).

If the high-pressure switch trips on a circuit with compres-

sors commanded on, the discharge pressure is sampled. If the

discharge pressure is between 368 and 418 psig, then the

discharge pressure trip point (Configuration

→

Cool

→

HPS.A,

HPS.B) is adjusted to the previously sampled trip point minus

3 psig. This is done to make a rough calibration of the high

pressure trip point which is used by the high discharge pressure

diagnostics.

When the trip happens, all mechanical cooling on the circuit

is shut down for 15 minutes. After 15 minutes, the circuit will

be allowed to come back on. An internal flag is set which needs

to sense the lead compressor on a circuit go from on to off, in-

dicating the circuit came back on after the 15-minute delay and

successfully completed a cooling cycle. If the high-pressure

switch trips again, the high pressure alarm occurs which will

then require a manual reset of the unit.

T072 (Evaporator Discharge Reset Sensor Failure) — This

sensor is responsible for third party reset of the cooling supply

air set point. If the unit is configured for “third party reset”

(Configuration

→

EDT.R

→

RS.CF=3) and this alert occurs, no

reset will be applied to the cooling supply air set point. Recov-

ery from this alert is automatic. Reason for error is either a

faulty sensor, wiring error, or damaged input on the CEM

board.