Testing Control Valve And Thermocouple - Desa CERAMIC PLAQUE Service Manual

V E N T - F R E E

Testing Control Valve and Thermocouple

The following procedure can be used to deter-
mine if the valve and thermocouple meet speci-
fication. This procedure requires a BASO milli-
volt tester. See Equipment, page 7.
PROCEDURE
1.
2.
3.
4.
Control
Valve
Figure 11. Testing Control Valve With
12
G A S
Connect the valve attachment to the con-
trol valve in place of the thermocouple.
Plug the valve attachment connector into
the BASO millivolt tester as shown in
Figure 11. Set BASO to 0-500 Milliamps.
Adjust the current to 80 ma (if using dry
cell batteries, set the current level by
adjusting the rotary volume knob).
Turn control knob from the OFF position
to the PILOT position. Check to see if the
control valve holds in satisfactory.
BASO
Milivolt Tester
500
0-1000
DC MILLIVOLT
MILLIVOLTS
Valve
Attachment
GRH/OV 032
BASO Milivolt Tester
Thermocouple
Attachment
H E A T E R S E R V I C E
5. If the control valve does not hold in,
increase current levels by 10 ma and
repeat step 4. Repeat by 10 ma incre-
ments until the valve holds in. Note re-
sult.
6. Gradually reduce ma level until the con-
trol valve drops out. Note result.
Hold-in current specification: 230 ma maximum
Drop-out current specification: 80 ma minimum
If the control valve operates correctly during the
above test, it is likely that the problem is the
result of a bad thermocouple.
7. Connect the thermocouple attachment
to the thermocouple as shown in Figure
12. Be sure the red clip is attached to the
outer (copper) thermocouple sheathing.
Set BASO to 0-500 Millivolts.
8. Light the burner pilot and continue to hold
the control knob down to keep the control
valve open, or remove the thermocouple
and hold it over an open flame (a BIC
MILLIAMPS
lighter can be used).
0-500
Thermocouple output specification: 20-28 mv
0-50
If the thermocouple millivolt output is below
ADJUST
specification, replace the thermocouple.
MILLIVOLTS MILLIAMPS
Figure 12. Testing Thermocouple With BASO Milivolt Tester
M A N U A L
BASO
Milivolt Tester
MILLIAMPS
500
0-500
0-1000 0-50
DC MILLIVOLTS
MILLIVOLTS
ADJUST
MILLIVOLTS MILLIAMPS
GRH/OV 031
Thermocouple
Attachment