Middleby Marshall PS224 PS310 PS360WB70/EWB with Midco burner, PS360WB70/EWB with Wayne burner

SECTION 3 - SERVICING COMPONENTS

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.

Figure 51

PS360WB70/EWB with Midco burner

Connects to

negative pressure side of air switch

•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 52

PS360WB70/EWB with Wayne burner

Connects to positive pressure side of air switch

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