Carrier appendix Insulate Suction Lines, Hot Gas Bypass, 38AUD Piping Connections

38AU

Table 6 – 38AUD 16-25 Piping Recommendations (Two-Circuit Unit)

NOTE: 38AUD requires TWO sets of refrigeration piping

R-410A	Equivalent Length
	Ft		0-38	38-75	75-113		113-150		150-188
	m		0-12	12-23	23-34		34-46		46-57
	Linear Length
	Ft		0-25	25-50	50-75		75-100		100-125
Model	m		0-8	8-15	15-23		23-30		30-38
38AUD*16	Liquid Line		1/2	1/2	1/2		1/2		1/2
	Max Lift		25	50	75		100		125
	Suction Line		7/8	11/8	11/8		11/8		11/8
	Charge ea. (lbs)
	Novation		11.7	13.8	15.7		17.6		19.6
	RTPF		21.7	23.8	25.7		27.6		29.6
38AUD*25	Liquid Line		1/2	1/2	1/2	5/8	1/2	5/8	1/2	5/8
	Max Lift		25	50	54	75	60	99	46	95
	Suction Line		11/8	11/8	11/8		11/8	13/8	13/8
	Charge (lbs) 1		19.3	21.0	23.0	26.0	25.9	29.7	28.0	32.7
		2	18.3	20.3	22.0	25.0	24.9	28.7	27.0	31.7
Legend:
Equivalent	Equivalent tubing length, including effects of refrigeration specialties devices
Length
Linear Length	Typical linear tubing length (50% added to linear to define Equivalent Length for this table)
Liquid Line	Tubing size, inches OD.
Max Lift	Maximum liquid lift (indoor unit ABOVE outdoor unit only), at maximum permitted liquid line pressure drop —
	S	Linear Length Less than 75 ft (23 m): Minimum 2.0° F subcooling entering TXV
	S	Linear Length Greater than 75 ft (23m): Minimum 0.5° F subcooling entering TXV
Suction Line	Tube size, inches OD
Charge	Charge Quantity, lbs. Calculated for both liquid line sizes (where applicable), but only with larger suction line size
	(where applicable)
NOTE:	For applications with equivalent length greater than 188 ft (57 m) and/0r linear length greater than 125 ft (38 m),
	contact your local Bryant representative.

Table 7 – 38AU Maximum Suction Pipe Size

Model:	Unit Size	Maximum Tube Size
38AUZ	16	15/8
	25	15/8
38AUD	16	15/8
	25	15/8

Vertical Separation (outdoor unit above indoor unit) –

Vertical elevation difference of 200 ft (60 m) is permitted when the outdoor unit (38AUZ or 38AUD) is located above the indoor unit.

Insulate Suction Lines —

Apply closed-cell tubular insulation to all suction lines between evaporator coil connection and 38AU unit’s suction service valve.

Hot Gas Bypass —

Hot gas bypass, if used, should be introduced before the evaporator. (A bypass route that also bypasses the evaporator circuit may lead to oil trapping in the evaporator circuit during low load conditions and then to oil slugging as evaporator load increases.) Model 38AU units do not include a hot gas stub connection; a tee must be field-supplied and

installed in the compressor discharge line. Run a 1/2-in OD line between outdoor unit and evaporator coil inlet. Install an Auxiliary Side Connector at the evaporator between TXV and distributor (follow instructions for the side connector part). Insulate the hot gas line.

38AUD: Generally only one hot gas bypass system will be applied on a two-circuit unit. Connect the hot gas bypass system to Circuit 1 (first-on/last-off, connected to the evaporator coil’s bottom circuit).

38AUD Piping Connections —

The 38AUD’s two circuits are designated Circuit 1 and Circuit 2. Circuit 1 is controlled by the thermostat’s Y1 (or TC1) contact and will be the first circuit on and last circuit off. Circuit 2 is controlled by the thermostat’s Y2 (or TC2) contact and this circuit is always the “lag” circuit.

See Fig. 6 for location of Circuit 1 and Circuit 2 service valves and field piping connections. Circuit 1 is on the left-hand side of the service valve compartment; Circuit 2 is on the right.

When a single piece evaporator coil with two separate circuits is connected to a 38AUD, the lower coil circuit should be connected to the 38AUD’s Circuit 1 so that the evaporator’s lower coil segment is first-on/last-off (to avoid re-evaporation of condensate on dry lower coil segments).

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