Carrier 39LG, 39LB, 39LD, 39LA, 39LC, 39LE, 39LF, 39LH03-25 specifications = 1.68 x .33 x

UNLOADING CONSIDERATIONS — Direct expansion coils can have two intertwined refrigerant circuits. In addition, quar- ter, half, full and double circuiting configurations are offered to allow optimum system performance and oil return at full and part-load operation.

Circuiting selection should result in a circuit loading of 0.8 to 2.0 tons per circuit at design load. Circuit loading must be evaluated at minimum load to ensure that it does not drop below 0.6 tons per circuit. Solenoid valves may be used, if nec- essary, to shut off the refrigerant supply to individual expansion valves to maintain adequate coil circuit loading.

Compressor minimum unloading and TXV quantity is nec- essary to determine minimum tonnage per circuit.

Minimum Unloading Equation:

(Tons/Circuit) x (Minimum Unloading)

x (Total # of TXVs)

# of TXVs Active

Example:

Condensing Unit: 38ARS012

Minimum Unloading:33%

Coil:	6 row, 11 FPI, Half Circuit
Coil Tons/Circuit:	1.68
Total TXVs:	2

In the first example we will determine the tons/circuit when both TXVs are active and the compressor is unloaded to its minimum of 33%.

	(1.68 Tons/Circuit) x (33% Minimum Unloading)
=	x (2 TXVs)
	2 TXVs Active

=(1.68) x (.33) x (2)

2

=.55 tons/circuit at minimum unloading UNACCEPTABLE

If we install a liquid line solenoid valve before one of the TXVs and close it so that only one TXV is active when the compressor is unloaded to its minimum of 33%, we see the following:

	(1.68 Tons/Circuit) x (33% Minimum Unloading)
=	x (2 TXVs)
	1 TXV Active

=(1.68) x (.33) x (2)

1

=1.10 tons/circuit at minimum unloading ACCEPTABLE

There are three different options to control tons/circuit when using an unloading compressor. The first is to use drop sole- noid valve control as illustrated above and let the suction cutoff unloaders “ride” with the load. The second is to use drop solenoid valve control as illustrated above with electric unload- ers and let the control algorithm determine the combination of solenoid valves and unloaders to limit tons/circuit to acceptable limits. The third is to limit the minimum amount of unloading so that tons/circuit is within acceptable limits.

SPECIAL PIPING WITH 4 SPLITS PER COIL

Manifolding for 2-Face Splits — Refer to Fig. 29 and exter- nally manifold as follows:

1.Connect the 4 expansion valves to the 4 distributors on each coil and connect the 4 suction lines to the 15-diameter-long risers as outlined in previous piping instructions.

2.Install common liquid line for upper face split to first (upper) and second expansion valves. Also, install a common suction line from suction lines attached to first (upper) and second suction header connections.

3.Repeat Step 2 for lower face split using third and fourth distributor and suction connections.

Manifolding for 2-Row Splits — Refer to Fig. 30 and exter- nally manifold as outlined for the 2-face splits with the following exceptions:

1.Manifold in pairs, the first and third coil connections for one split.

2.Manifold the second and fourth pairs of coil connections for the other split.

NOTE: Split section using first and third pairs of coil connec- tions should be first on, last off for coils with right hand (facing direction of airflow) connections and the reverse for left hand connections.

Hot Gas Bypass Connection with 4 Splits per Coil — For either face or row splits connect a hot gas bypass auxiliary side connector to each distributor of coil split that is first on, last off. Refer to installation instructions for Hot Gas Bypass.

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