TRANE- q Genera RTAA-SB-4 lit l Service Bulletin . Library S ervice Literature Prod uct Section Refrigeration Product Rotary Liqu id Chillers - A/C Model RTAA Literature Type G enera l Service Bu l leti n Sequence 4 Date October 1991 File No. SV-RF-RLC -RTAA-SB-4-1091 Supersedes

Subject: Sl ide Valve Operation and Troubleshooti ng 0

Introducti on :

The purpose of this bulletin is to provide information that is required to troubleshoot the slide valve operator on CHHB compressors .

Discussion :

The Air Cooled Series R Chiller (RTAA) is designed with 2, 3, or 4 compressors, that include modulating slide valves, that vary the capacity of the compressor.

The slide valve is operated by a piston/cylinder assembly. The piston/cylinder assembly is powered by oil pressure that is regulated by two "normally closed" solenoid valves. These valves are called the load and unload solenoid valves (Note: The load solenoid valve is mounted closest to the compressor motor). The coil on each solenoid valve is 110 VAC. Reference Figure 1, to view a schematic of the slide valve hydraulic system. W A C

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Since the Trane Company has a policy of continuous product improvement, it reserves the right to change specifica- O Ame rican Standard I nc - 1991 tions and design without notice. The installation and servicing of the equipment referred to in this booklet should be done by qua7ified, experienced technicians. Fig ure 1 Typ ical Sli d e Va l ve H ydrau l ic Syste m

To Ff 0171 ^ Compressor Oil Suction SuppI Y to

U L Unlaading L o a aing Solenoid Vafve So l e n o id V a 1 ve

Stide Valve Piston - Slide Valve Shaf t Schroder Valve Piston/Cylinder Assembly Access Sl i de Valve 77-P Load f

I* Li_/^^1,11 L ^1 Compressor Rotor

The microprocessor controls operate the load and unload solenoid valves, in response to varying demands for capacity. On an increase demand for capacity, the load solenoid valve is energized (pulsing 110 volts); allowing oil pressure to enter the piston/cylinder section, moving the piston, which moves the slide valve via the slide valve shaft over the compressor rotors , and loads the compressor.

On a decrease demand for capacity, the unload solenoid valve is energized (pulsing or constant 1 1 0 VAC, which is dependent on the mode of the microprocessor controls), which relieves the oil pressure that was built up in the piston/cyli nder section, retracting the piston, which pulls the slide valve via the sl ide valve shaft away from the rotors, and unloads the compressor.

On a hold demand for capacity, both the load and unload solenoid valves remain deenergized, which maintains the positon of the piston and slide valve.

Why Does The Slid e Va lve Move? 0 There are four forces that act upon the slide valve/piston assembly. See Figure 2.

2 Figure 2 Typical Slide Valve/ Piston Assembly

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10 Pisto„

Load F^31

Slid t Valv e Sucti o n Regulated Pr e ssur e Pressure A FF,`/-/77777 71 Q '1-1-' C '•

Discharge Pressure ILLLLLLL .L/_.J A - Slide Valve-Suction Pressure B - Slide Valve-Discharge Pressure C - Piston-Discharge Pressure D - Piston-Regulated Pressure

0 For example, if the piston or shaft were not attached to the slide valve, the discharge pressure and suction pressure, present at either end of the slide valve, will force the slide valve over the rotors, and load up the compressor.

However, there is a piston connected to a slide valve via a slide valve shaft. The piston provides more surface area, than the slide valve ends. The discharge pressure and suction pressure present at both ends of the piston, will force the piston to overcome the slide valve movement in the opposite d i rection , thus, pulling the slide valve away from the rotors and unload the compressor .

To load and modulate the compressor, oil pressure is added and subtracted via load and unload solenoid valves to the cylinder side of the piston. This pressure balances the other 3 forces, and allows positioning of the slide valve over the rotors, to obtain varying degrees of compressor capacity.

Troubleshooting Slide Valve Operation

Oil pressure suppl y to the load solenoid valve is tapped from the bearing and rotor injection oil suppl y li ne. Due to pressure drop of the oil cooler, angle valve, oil filter, master solenoid valve, etc., the oil pressure supply to the load solenoid valve will be approximately 20 - 30 PSIG below compressor refrige rant discharge pressure.

Schraeder The Schraeder valve is mounted on the discharge end of the compressor. See Figure 3. Oil pressure at the hold valve is not proportional to the position of th e slide valve, however, the oil pressure will be whatever it takes to valve coils, the slide valve at a given position. Th e wiri ng to the microprocessor, from the load and unload solenoid or jumpered to maintain a constant position of the valves, to prove the operation of the slide valve. ^ can be removed Figure 3 Schraeder Valve Location on Compressor Discharge End

0 Unload Solen o id Val ve Load Solenoid Valve

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Piston/Cylinder Assembly Access Schraeder Valve

The following tests assume the electrical circuits to the load/unload solenoid valve coils are correct and operative. An audible "click" can be heard when the valve is energized, and the magnetism created by an energized coil will attract the tip of a pocket screwdriver. Insure the valves are electrically correct before proceeding.

Load and Unload Solenoid Valves Checkout

A. Connect a gauge to the piston/cylinder access Schraeder valve and start compressor.

B. Apply constant power to load solenoid valve coil. Leave unload solenoid valve coil attached to microprocessor. Pressure should rise to within 20-30 PSIG of condenser pressure, provided microprocessor does not energize unload solenoid valve, due to a limit or temperature control. If pressure fails to rise, suspect one of the following:

1. Clogged oil filter 2. Plugged load solenoid valve 3. Leaking unload solenoid valve (verify there is no signal from controls to be energized).

4 C. Disconnect power from both solenoid valve coils. Pressure should maintain. If pressure drops, suspect a leaking load solenoid valve.

^ D. Energize unload solenoid valve, until pressure drops to about halfway between suction and condenser pressures, then insure that power is not applied to both valves. Pressure should maintain. If pressure rises, suspect a leakin g load solenoid valve. If pressure drops, suspect a leaking unload solenoid valve.

^ E. Put constant power to unload solenoid valve coil. Disconnect power to load solenoid valve coil. Pressure shoufd drop to suction pressure, if pressure does not drop, suspect a plugged unload solenoid valve.

If either a leaking load or unload solenoid valve is suspected of a problem, a piece of shimstock can be placed between the valve and the gasket, sealing off the ports of the valve. This will essentially isolate the valve from the system, to confirm diagnosis of a leaking solenoid valve.

If either a plugged load or unload solenoid valve is suspected, replacement of valve is required to confirm diagnosis.

Slide Valve Movement

If the load/unload solenoid valves operate properly, but the compressor motor amperage fails to rise, or fall, in response to commands from the load/unload solenoid valves, the slide valve piston could be hesitant to move. This usually happens when the compressor is first put into service, and the rings on the piston have not been "broke-in" yet.

To move slide valve, perform the following sequence: o 1 - The discharge pressure can be increased to acquire more pressure to move the slide valve. Disconnect wiring to several condenser fan motor contactor coils, in order to achieve 350-370 PSIG condenser pressure. Typically, this will provide sufficient power to move a"hesitant" slide valve piston.

2 - If the slide valve is still failing to move, an extra 20-30 PSIG that is lost, via the oil cooler circuit, can be acquired by deenergizing the load solenoid valve, and temporarily connect a refrigerant service gauge set, between the compressor refrigerant discharge Schraeder valve and the Schraeder valve for the piston/cylinder assembly. The valve on the gauge set can be used to simulate the load solenoid valve.

3 - If the slide valve still fails to move, access to the top of the piston can be gained, through the Schraeder valve piston/cylinder access port, by using the following procedure:

A. Isolate compressor via compressor suction and discharge service valves.

B . Relieve pressure on compressor down to 2 PSIG .

C. Remove complete piston/cylinder access Schraedervalve. (Note: The threads on this valve is sealed with loctite. Care must be taken to not damage, or break valve off when removing).

D_ Insert a smooth rod (to prevent damage to pipe threads), that has a diameter of no more than 5/16" (i.e.,Philips screwdriver). If slide valve is in the unloaded positon, insert the rod (approximately 3/4") to make contact with the piston. Next, push on the piston and the slide valve should move to the loaded position. Table 1 lists the stroke lengths of the various compressors and slide valves. A slight tap with a hammer may be required to get the piston moving.

E Table 1 Slide Valve Stroke Length s Com ressor CHH B 070 3 Inches 3.25 Inches • CHH B 100 3.5 Inches

E. To return the piston to the unloaded position, add pressure to the compressor, via the suction service valve. This pressure will be on the back side of the piston, thus, causing its movement back to the unloaded position. i

F. Repeat steps D adn E to insure free movement of slide valve/piston assembly.

G. Evacuate any portion of the compressor that non-condensibles may have entered.

H . Open service valves and put compressor back into operation .

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