Test Procedure-Trouble Analysis - McQuay MicroTech Unit Controller Installation And Maintenance Data

TEST PROCEDURE - TROUBLE ANALYSIS
Numbers below coincide with numbers shown in the right
hand column of the Trouble Symptom Chart.
System or chiller operating problems are not described.
Check the MicroTech display and fault history, or see the IM
for the unit involved for chiller problems.
All of the following assumes that power is applied to the
MicroTech Station panel and the circuit breaker is on.
Where the following procedures describe the removal and
replacement of fuses, connectors, terminals or jumpers,
always shut off the power to the panel before making the
disconnect or replacement.
1. If the control EnGinn LED is out, or if the LED is on but
does not blink, check for the presence of 17 VDC enter-
ing the control EnGinn, and for 5 VDC leaving. Voltage
readings should be measured by connecting the power
lead of the voltmeter to the appropriate solder plug on
the mother board, and the common meter lead to the
ground screw in the control back panel.
Solder plugs to be tested are approximately 1 inch in from
the right hand edge of the mother board, and in the ap-
proximate vertical center.
One solder plug is to the left of the words "12 VAC". This
plug should read, 17 VDC. Directly above this plug is
another marked "5 VAC". A test at this plug should show
5 VDC.
If the lower plug test delivers a reading of 17 VDC, and
the upper test plug shows less than 5 VDC, the problem
is either in the power cartridge or the mother board.
Substitute a new power cartridge for testing before replac-
ing the mother board.
2. If the test above confirms the presence of 17 VDC enter-
ing the Control EnGinn, and 5 VDC leaving, the problem
will probably be either a faulty logic cartridge, or a bad
mother board. Substitute a new logic cartridge before
replacing the mother board.
3. To test for a blown fusible link in the #2 transformer, with
the circuit breaker tripped off (white sleeve showing),
disconnect the red striped yellow lead from the terminal
number 85. Re-apply power, and check for 12 volts AC
between the exposed end of the red striped yellow lead,
and terminal number 83 or 84.
If no voltage is indicated, verify that the meter is func-
tioning or that the transformer is otherwise delivering
power by reading between terminals 83 and 84. (Read
24 VAC).
Replace a defective transformer.
4. To test the daughter board fuse, read 17 volts DC bet-
ween the left side terminal clip at the fuse outlet and the
back panel ground. If no voltage is present, move the
power test lead of the meter to the right side fuse clip.
If 12 volts DC is present at one end of the fuse, and
0 to 1.9 volts at the other, the fuse is bad. Replace it.
If no voltage is present to ground on either side of the
fuse, or very low voltage exists on both sides, check the
transformer #3 fusible link (See #5, below).
If the transformer fusible link is okay and no voltage
or very low voltage exists on both ends of the fuse, the
fuse is okay, but the daughter board may be bad. If so,
replace it.
5. To test the transformer #3 fusible link, interrupt the power
to the panel and lift the TS2 terminal strip off the daughter
board pins. Re-apply power to the panel, and measure
for voltage between TS2 terminals #2 and #4, or #3 and
#4. Voltage should read 12 VAC If it does not, replace
the transformer.
6. The daughter board contains 12 LED's to visually depict
closure of the multiplexed digital inputs. Figure 30, page
42, lists these safety devices and the LED number assoc-
Page 40 / IM 403
iated with each.
If a daughter board LED is lit, yet the display statement
shows that contact to be open, it's possible that the
daughter board itself may be bad. To check the daughter
board, using a DC voltmeter, read the voltage across the
daughter board capacitors (mounted below LED's). If the
LED is lit, voltage should approximate 30 VDC. If the LED
is out, voltage should be zero.
If widely different values are present, before condem-
ning the daughter board, check to be sure a diode, part
number 350A034H04, has been installed between ter-
minals 1 and 8 on terminal strip TS2. If not, add this diode
following the instructions on page 35 ("Daughter Board
Ground Wire Diode"). Then retest the voltage at the
capacitor. If the voltage is still not correct, check the diode
and replace it or the daughter board.
7. Hex switch settings must be correct for the combination
of equipment connected. See the text and Table 11 in the
main body of this IM.
8. The microprocessor LED located on the keypad cover
is replaceable. See Replacement parts data for the cor-
rect part number.
9. To check a suspected bad display EnGinn, interrupt
power to the panel then disconnect the power plug from
the top right hand side of the display EnGinn. Re-apply
power to the panel. Read the voltage at the plug.
At the plug pins 3 to 2, read 12 VAC.
At the plug pins 3 to 1, read 12 VAC.
At the plug pins 1 to 2, read 24 VAC.
If readings are not as described, replace transformer
#2.
If readings are as described, interrupt power to the
panel and reconnect the power plug to test for 5 volts
DC to ground. Re-apply power to the panel. A test voltage
connection may be made at the 5 volt DC solder plug
on the right side of the display EnGinn directly above the
communications cable port.
If 5 volts DC is not available, replace the Display
EnGinn.
If a replacement is not immediately available, it's possi-
ble that the chiller may be operated with a minor control
modification. See the text describing the watchdog circuit.
10. Control panels with software versions number 07 and later
(see software identification information) require a
minimum amps consumption, following the 30 second
"MCR is on" starting sequence. The minimum amps
draw will be between 5% and 15% of compressor Rated
Load Amps (RLA) and if unchanged from the factory set-
point, will be 10% of RLA.
If something in the MCR circuit, not included in the
Multiplex digital inputs (daughter board LED) circuits,
prevents the MCR coils from energizing, the display may
assume the MCR coils were energized, but because of
the low current measured, scheduled an orderly
shutdown.
If this circumstance occurs, inspect those devices or
connections not overseen separately. These include the
fuses in the number 14 and number 3 output relay cir-
cuits, the relays themselves, the MCR coils and intercon-
necting 115 VAC control wiring.
To test the solid-state relay fuses, with the LED "off",
disconnect the lead at the odd numbered relay terminal.
Using a voltmeter read AC voltage from the odd
numbered terminal to ground. Voltage read should be the
same as the reading from the even numbered terminal
to ground.
If no voltage is read from the odd numbered terminal
to ground when voltage is applied to the even numbered
terminal, and the one lead is disconnected as noted