Carrier 19XR Start-up, Operation And Maintenance Instructions Manual

Also see for HERMETIC CENTRIFUGAL LIQUID CHILLERS 19XR: User manual Start-up and service instructions Installation instructions Product data Installation instructions

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Carrier 19XR Start-up, Operation And Maintenance Instructions Manual Manual pdf 83 page image

5. Using an ohmmeter, perform the following resistancemeasurements and record the results:MEASUREBETWEENSCR PAIRSBEINGCHECKEDRECORDEDVALUET1 and T6 3 and 6T2 and T4 2 and 5T3 and T5 1 and 4If all measured values are greater than 5K ohms, pro-ceed to Step 10. If any values are less than 5K ohms,one or more of the SCRs in that pair is shorted.6. Remove both SCRs in the pair (See SCR Removal/Installation).7. Using an ohmmeter, measure the resistance (anode tocathode) of each SCR to determine which device hasfailed.NOTE: Both SCRs may be defective, but typically, onlyone is shorted. If both SCRs provide acceptable resis-tance measurements, proceed to Step 10.8. Replace the defective SCR(s).9. Retest the ‘‘pair’’ for resistance values indicated above.10. On the right side of the firing card, measure the resis-tance between the red and white gate/cathode leads foreach SCR (1 through 6). A measurement between 5 and50 ohms is normal. Abnormally high values may indi-cate a failed gate for that SCR.If any red or white SCR gate leads are removedfrom the firing card or an SCR, care must be takento ensure the leads are replaced EXACTLY as theywere (white wires to gates, and red wires to cath-odes on both the firing card and SCR), or damageto the starter and/or motor may result.11. Replace the SCRs and retest the pair.SCR REMOVAL/INSTALLATION — Refer to Fig. 39.1. Remove the SCR by loosening the clamping bolts on eachside of the SCR,2. After the SCR has been removed and the bus work is loose,apply a thin coat of either silicon based thermal joint com-pound or a joint compound for aluminum or copper wireconnections to the contact surfaces of the replacement SCR.This allows for improved heat dissipation and electricalconductivity.3. Place the SCR between the roll pins on the heatsink as-semblies so the roll pins fit into the small holes in eachside of the SCR.NOTE: Ensure the SCR is installed so the cathode side isthe side from which the red wire extends. The heatsink islabeled to show the correct orientation.4. Hand tighten the bolts until the SCR contacts theheatsink.5. Using quarter-turn increments, alternating between clamp-ing bolts, apply the appropriate number of whole turnsreferencing the table in Fig. 39.Care must be taken to prevent nut rotation while tight-ening the bolts. If the nut rotates while tighting thebolt, SCR replacement must be started over.6. Reconnect the red (cathode) wire from the SCR and thewhite (anode-gate) wire to the appropriate location onthe firing card (i.e., SCR1 wires to firing card terminalG1-white wire, and K1-red wire).7. Reconnect all other wiring and bus work.8. Return starter to normal operation.LOOSENANDTIGHTENBOLTSFROMTHIS ENDCLAMPINGBOLTNUTALUMINUMHEATSINKROLL PINSCRASCR PARTNUMBERBISCRCLAMPSIZEADIMENSION(in.)NO OFTURNSBOLTLENGTH(in.)6601218 1030 2.75( 70 mm) 11⁄ 2 3.0( 76 mm)6601818 1030 2.75( 70 mm) 1 1⁄ 2 3.0( 76 mm)8801230 1035 2.75( 70 mm) 1 3⁄ 4 3.5( 89 mm)8801830 1035 2.75( 70 mm) 1 3⁄ 4 3.0( 89 mm)15001850 2040 4.00(102 mm) 2 3⁄ 4 4.0(102 mm)15001850 2050 4.00(102 mm) 2 3⁄ 4 5.0(127 mm)220012100 Consult Benshaw Representative330018500 Consult Benshaw RepresentativeFig. 39 — SCR Installation83