Carrier 42CA Installation, Start-Up And Service Instructions Manual page 52

Adjusting the low, medium, and high potentiometers re-
quires the use of a multi-meter capable of measuring 0~5 vdc.
1. Only trained and qualified individuals should attempt to
adjust or service components on any electrical compo-
nent. Failure to follow safety rules could result in electri-
cal shock or hazard.
2. Unit must be powered to perform the following proce-
dure. If main power is not available, connecting a tempo-
rary 24V-40VA power supply to parallel with a secondary
outputs of the unit's transformer is recommended.
3. Set the electrical multi-meter to volts direct current (vdc)
on the 0~5 or 0~20 vdc scale.
4. Attach black (negative) lead of meter to the DC common
terminal, labeled "L2" above the potentiometer and to the
left of the orange relay.
APPENDIX A — POTENTIOMETER ADJUSTMENT
Fig. A — 3-Speed ECM
5. Attach the red (positive) lead of the meter to the red wire
that bridges the 0-10 vdc outputs: high, medium, and low.
6. High Speed: Close high speed relay by applying 24-v to
the high terminal. Using a small screwdriver turn the
VR3 potentiometer so the meter measures 4.51 vdc. This
will set the ECM speed to 90% of maximum for high
speed. Open the high speed relay.
7. Medium Speed: close medium speed relay by applying
24-v to the medium terminal. Using a small screwdriver
turn the VR2 potentiometer so the meter measures
3.53 vdc. This will set the ECM speed to 70% of maxi-
mum for medium speed. Open the medium speed relay.
8. Low Speed: Close low speed relay by applying 24-v to
the low terminal. Using a small screwdriver turn the VR1
potentiometer so the meter measures 2.06 vdc. This will
set the ECM speed to 40% of maximum speed for low
speed operation. Open the low speed relay.
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