Carburettor Heater; Trouble Shooting - Husqvarna 390XP Workshop Manual

11.2 Hand grip heater and

carburettor heater 390

Some chainsaws are fitted with hand grip heaters and
carburettor heaters, and consist of the following parts:
• Generator.
• Switch.
• Heating element in rear hand grip.
• Front hand grip with heating element.
• Carburettor heating element.
• Thermostat.

11.2.1 Trouble shooting

Trouble shooting can be done with most components
fitted on the saw. Trouble shooting require:
• ammeter
• ohmmeter
• cooling spray
The most common fault is oxidisation of the heating
element contacts in the rear hand grip and the switch
contact. To trouble shoot:
Heating element in rear hand grip.
Separate the cable connection at B. See fig. 10. Remove
the switch with a screwdriver. See fig. 9. Set the switch
to position "0".Clean the contacts D, E, F and G. See
fig. 10. Measure the resistance between point B and F,
between D and C and between E and C. See fig. 10. The
resistance for both heating elements should be 0.6-
2.4 ohms. Between D and C and between E and C the
resistance should be 0.3-1.2 ohms. Replace the element
if the values deviate.
Front hand grip with heating element
Measure the resistance in the front hand grip element
between points A and B. See fig. 10. The ohmmeter
should show 3-4 ohms. If the value is higher, replace the
hand grip.
Generator
Measure the resistance in the generator between the
points G and H. See fig. 10. The ohmmeter should show
0.3-1.3 ohms. If the value is higher, replace the genera-
tor.
Switch
Release one of the connections to the switch and con-
nect the ohmmeter between the points F and G. See fig.
10. The ohmmeter should show more than 1000 ohms
with the switch in position "0". The ohmmeter should
show at least 0.1 ohms with the switch in position "1".
Replace the switch if the values deviate.
Carburettor heating element
Measure the resistance for the heating element on the
carburettor at L and J. The ohmmeter should show 3-10
ohms. Replace the heating element if the value deviates.
Thermostat
Release the earth cable J. Measure with the amme-
ter between J and K. Start the saw and run at approx.
10,000 rpm. The ammeter should show 0 at an air tem-
perature of 15 C or higher. Cool the thermostat with a
cooling spray. The ammeter should show 2 A at 10,000
rpm. Replace the thermostat if the values deviate.
Fig. 9
Fig. 9
Fig. 9
A
A
B
B
F
F
G
G
Fig. 10
Fig. 10
Fig. 10
Electrical system
C
C
D
D
E
E
H
H
L
L
J
J
K
K
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