Preheated Air - New Control Method
Section2
Group
25
No.
818
Date
August 1997
Preheating air
850
REFERENCE: TP 2101201, SECTION 2 (20-22, 25-26) B5204, B5234, B5252, B5254 ENGINES; 850 1992-
This Service Bulletin supplements section "Group 25 Intake and exhaust systems, paragraph CA. Preheating Intake air. check" in Service Manual TP 2101201.
Write In "Also see Service Bulletin 2-25-818" Immediately beneath the heading "CA. Preheating Intake air, check" in Service Manual TP 2101201.
New control method for preheating air
The design and function of the preheating air system, fault-tracing, and procedure for replacing components, are all described in this Service Bulletin.
The system controls the intake air temperature so that it remains between +27°C (81°F) and +37°C (99°F) in the 850.
Function
The intake manifold vacuum in the plastic tubes is distributed from the multi-nipple (1) via a bimetal sensor-controlled damper (2) to a vacuum tank (3) which controls a damper, which opens and lets hot air into the cold intake air. When the throttle is wide open no vacuum is created and the air damper remains closed.
When the outside temperature is cold and with wide open throttle (WOT), the center damper is held open by a wax thermostat (4), which is located between the vacuum tank and the center damper.
Checking the system
Remove:
- cold air hose.
Check:
- that all vacuum tubes are properly connected
- that the tubes are not broken
- that the tubes are not creased or pinched
- that the wax thermostat opens the damper 10 mm (40) (see illustration) at the warm air terminal after 1 hour at 20°C (68°F)
- that the valve regulating the hot air supply, should with the engine running, and a surrounding temperature of below +27°C (81°F), move towards cold air closed. (All the air should come from the preheating plate).
- the valve that is dosing the warm air supply should be 10 mm (3/8") open after 1 hour at -20°C (-4°F).
Important Position the tube in the clamp as illustrated on C.
When replacing vacuum tubes
Remove:
- cover over the control pulley
- clamp
- the defective tube without using tools
Install:
- new tube (A) between the throttle body (TB) and bimetallic sensor as illustrated
- new tube (B) between the bimetallic sensor and terminal at the engine
- clamp (C)
Important:
Position the tube in the clamp as illustrated.
- cover over the control pulley.
WARRANTY STATEMENT:
Claims may be submitted under the New Car Limited Warranty when a manufacturing defect is present using clam type: 01
Operation No. Labor description Time allowance
25918-2 Preheating air, check 0.3 hr
25437-2 Replacing vacuum tubes, terminals 0.2 hr