22
Heat Exchanger Replacement – The heat exchanger is the
largest and most expensive item in the furnace. Before
replacing the heat exchanger, make certain it is the problem.
Call the technical service department if you have any uncer-
tainty about a heat exchanger failure. Heat exchangers can
become sooted up due to debris in top of furnaces,
improper conversion, or not being converted to LP. See
troubleshooting section on flue and conversion section of
this manual. This condition is not covered under warranty.
To Test Heat Exchanger:
Several methods may be used to test, or inspect for heat
exchanger flaws.
1.
Remove the blower and burner. Visually inspect the heat
exchanger with a mirror. If you find a crack or hole in any
part of the heat exchanger, replace with out delay.
2.
When the blower starts, observe the flame. If there is a
disturbance in the flame, inspect and determine the
cause.
3.
Using a CO detector from the nearest register, monitor
the level for an increase while the unit runs. Single digits
of CO are common, but cigarette smoke, etc. can have an
impact on the level. A rapid increase in the CO level while
the furnace is running is not normal. If this occurs inspect
the heat exchanger.
Note: The furnace does not have to removed from its alcove
to replace the heat exchanger. Be sure to order the replace-
ment gasket kit along with the heat exchanger. It contains all
gaskets used in the furnace.
Change Out Procedure:
1.
Disconnect all gas and electrical power to furnace.
2.
Disconnect flue.
3.
Remove burner assembly.
4.
a. M1G-056-070 Only: Remove combustion air pipe.
b. M1G-077-090 Only: Remove combustion air pipe and
combustion blower.
5.
Remove blower assembly.
6.
Remove blower deck panel. NOTE: Panel will be difficult
to remove with furnace in alcove.
7.
Remove front panel. NOTE: One of the panel screws is
located through the combustion air box on the right.
8.
Lift up divider panel out of side cabinet lances.
9.
Support the underside of the heat exchanger with a
board.
10. Remove top collector panel. NOTE: Two screws attach
through top of cabinet.
11. Remove the other eight screws in the top of the cabinet
that hold the combustion air box.
12. Remove heat exchanger and replace.
13. Reverse steps one through eleven to reinstall.
NOTE: Be sure to install all new gaskets (from gasket
replacement kit).
14. Start up and check out for proper operation.
Figure 17. Heat Exchanger
Roll Out Switch - (M1G* - 056 & 070) The furnace is
protected by a manual reset safety switch located on the
bottom left hand side of the combustion pipe. A draft imbal-
ance or improperly staging valve can cause this switch to
open up. Check for poor draft or blockage in the heat ex-
changer to correct draft imbalance.
Pilot Outage – Pilot outage can occur because of either a
mechanical (internal) or environmental (external) problem.
The frequency and conditions that exist will be important
information in solving a pilot outage problem. Most mechani-
cal problems will result in a situation where pilot can not be lit
at all or goes out with the first cycle or shortly thereafter. The
environment around the furnace or home will be trickier to
diagnose and usually will have infrequent occurrences of pilot
outage, such as once a week, only on windy days etc. Since
most pilot outage problems fall under one of these two
situations our troubleshooting will be divided up into these two
areas. See Pilot Outage chart, next page.
