22
INSTALLER’S GUIDE
18-HE39D8-13A-EN
Honeywell W7459 Only - Troubleshooting - Mixed Air Sensor
Resistance should
match table in Installer's
Guide.
Repair or replace
MAS
Dampers drive to
100% open although
the mixed air temp is
below 55F.
Remove MAS
wires from "T" and
"T1" terminals on
logic module.
What is
It can be possible for the tip
of the MAS to twist near the
thermistor which causes the
leads to short and indicate a
low resistance reading
resistance of
MAS?
Less than 3.5 ohms
Greater than 3.5 ohms
