Bryant 577D----A installation instructions Final Checks, Resistance Values Versus Temperature

exists, the thermal protector is open. The control de-energizes the compressor contactor for 15 minutes, but continues to operate the outdoor fan. The control Status LED will flash the appropriate code shown in Table 4. After 15 minutes, with a call for low or high stage cooling, the compressor contactor is energized. If the thermal protector has not re-set, the outdoor fan is turned off. If the call for cooling continues, the control will energize the compressor contactor every 15 minutes. If the thermal protector closes (at the next 15 minute interval), check the unit will resume operation.

If the thermal cutout trips for three consecutive cycles, then unit operation is locked out for 4 hours and the appropriate fault code is displayed.

NO 230V AT COMPRESSOR

If the compressor voltage is not sensed when the compressor should be starting, the contactor may be stuck open or there is a wiring error. The control will flash the appropriate fault code. Check the contactor and control box wiring.

TROUBLESHOOTING UNIT FOR PROPER SWITCHING BETWEEN LOW & HIGH STAGES

Check the suction pressures at the service valves. Suction pressure should be reduced by 3-10% when switching from low to high capacity.

NOTE: The liquid pressures are very similar between low and high stage operation, so liquid pressure should not be used for troubleshooting.

Compressor current should increase 20-45% when switching from low to high stage. The compressor solenoid, when energized in high stage, should measure 24vac.

COMPRESSOR INTERNAL RELIEF

The compressor is protected by an internal pressure relief (IPR) which relieves discharge gas into compressor shell when differential between suction and discharge pressures exceeds 550 - 625 psi. The compressor is also protected by an internal overload attached to motor windings.

TEMPERATURE THERMISTORS

Thermistors are electronic devices which sense temperature. As the temperature increases, the resistance decreases. Thermistors are used to sense outdoor ambient (OAT) and coil temperature (OCT). Refer to Fig. 28 for resistance values versus temperature. See Fig. 29 for OCT location.

If the outdoor ambient or coil thermistor should fail, the HP/AC control will flash the appropriate fault code (See Table 4).

IMPORTANT: Coil thermistor is factory mounted. Check to insure thermistor is mounted properly. Outdoor air thermistor (OAT) is field mounted and connected. Verify that the OAT has been properly installed.

THERMISTOR CURVE

	90
(KOHMS)	80
	70
	60
RESISTANCE	50
	20
	40
	30

10

0

0	20	40	60	80	100	120
		TEMPERATURE (DEG. F)

A91431

Fig. 28 - Resistance Values Versus Temperature

THERMISTOR SENSOR COMPARISON

The control continuously monitors and compares the outdoor air temperature sensor and outdoor coil temperature sensor to ensure proper operating conditions. The comparison is:

S In cooling mode, if the outdoor air sensor indicates ≥ 10 _F (5.5_C) warmer than the coil sensor (or) the outdoor air sensor indicates ≥ 20_F (11.0_C) cooler than the coil sensor, the sensors are out of range.

SIn heating if the outdoor air sensor indicates ≥ 35_F (19.3_C) warmer than the coil sensor (or) the outdoor air sensor indicates ≥ 10_F (5.5_C) cooler than the coil sensor, the sensors are out of range.

If the sensors are out of range, the control will flash the appropriate
fault code as shown in Table 4.
The thermistor comparison is not performed during low ambient
cooling operation.
FAILED THERMISTOR DEFAULT OPERATION	A
Factory defaults have been provided in the event of failure of	--
	--
outdoor air thermistor and/or coil thermistor.
	577D
If the OAT sensor should fail, low ambient cooling will not be
allowed and the one-minute outdoor fan off delay will not occur.
Defrost will be initiated based on coil temperature and time.
If the OCT sensor should fail, low ambient cooling will not be
allowed. Defrost will occur at each time interval during heating
operation, but will terminate after 5 minutes.
If there is a thermistor out of range error, defrost will occur at each
time interval during heating operation, but will terminate after 5
minutes.
Refer to the Troubleshooting Chart (Table 9 and 10) for additional
troubleshooting information.

A06311

Fig. 29 - Outdoor Coil Thermistor (OCT) Attachment

FINAL CHECKS

IMPORTANT: Before leaving job, be sure to do the following:

1.Ensure that all wiring is routed away from tubing and sheet metal edges to prevent rub-through or wire pinching.

2.Ensure that all wiring and tubing is secure in unit before adding panels and covers. Securely fasten all panels and covers.

3.Tighten service valve stem caps to 1/2-turn past finger tight.

4.Leave Users Manual with owner. Explain system operation and periodic maintenance requirements outlined in manual.

5.Fill out Start-Up Checklist located at the back of this manual and place in customer file.

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