Middleby Marshall PS200 series - Manual (Page 83)

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1. Original-style round air switch with screw adjustment
(P/N 28023-0005)
This was the standard switch used through 9/96 and is
no longer available. If it must be replaced, use Kit P/N
35624 (for use in the USA) or 35625 (for export use).
See #2 below for a description of these kits.
2. Dungs square-case air switch with dial adjustment
This was the standard switch used from 9/96 through
1/02. It cannot be upgraded to the current Yamatake-
Honeywell octagonal switch, and so should still be used
as a service replacement. EXCEPTION: PS570G and
all PS555 ovens have used the Yamatake-Honeywell
switch throughout their production run (see #4 below).
Two different models were used; one for domestic ov-
ens, and another for export ovens. The switches are
identical except for the markings on the dial. The do-
mestic unit measures pressure in water column inches
(in. W.C.), while the export unit measures pressure in
millibars (mbar).
•
Domestic switch: Kit P/N 35624
• Export switch: Kit P/N 35625.
3. Dungs square-case “alternate” air switch with threaded
screw-type adjustment (P/N 36194)
This switch was used on a limited number of domestic
production ovens in early 1997 to cover an availability
problem with the standard switch (see #2 above). Mark-
ings were in water column inches (in. W.C.). An export
version of this switch was never used.
This switch was never available as a service part. If it
must be replaced, use Kit P/N 35624 (see #2 above).
4. Yamatake-Honeywell air switch, non-adjustable
This switch is the current standard for all new-produc-
tion Middleby ovens. You may NOT use this switch as
an upgrade on an oven equipped with an older switch.
Two different models are used; one for dometic and
standard export ovens, and another for CE-approved
ovens.
• Domestic switch: P/N 39530
• CE-version switch: P/N 37498
If this switch must be replaced, use an identical switch.
Note that this is the ONLY time that you may use P/Ns
39530 and 37498 as service replacement parts.
B. Troubleshooting
1. Postive pressure vs. negative pressure
All air switches except the original round version can
sense either positive air pressure or negative air pres-
sure. The connection that is actually made to the switch
depends on the application.
•
If the switch is used to detect blower operation, the
tip of the pitot tube is located outside of the blower
wheel. This means that the pressure applied to
the end of the tube is positive. Because of this,
the tube should be connected to the positive side
of the switch.
• If the switch is used to detect burner blower opera-
tion, check the type of burner used on the oven.
-
The Midco burner, used ONLY on some
PS360EWB and PS360WB70 ovens, has its
pitot tube mounted inside the blower wheel.
For correct operation, you should attach the
tube to the NEGATIVE side of the switch.
Refer to Figure 51 for an illustration of the Midco
burner.
- For ovens with the standard Wayne burner, the
pitot tube is mounted outside the blower wheel.
For correct operation, you should attach the
tube to the POSITIVE side of the switch.
Note that some PS360EWB and PS360WB70
ovens use the Wayne burner. You should al-
ways check the type of burner installed into
the oven before connecting the air tube. Refer
to Figure 52 for an illustration of a typical
PS360WB70/EWB gas train with the Wayne
burner.
Figure 51
PS360WB70/EWB with Midco burner
Figure 52
PS360WB70/EWB with Wayne burner
Connects to
negative pressure
side of air switch
Connects
to positive
pressure
side of air
switch
SECTION 3 - SERVICING COMPONENTS