Function of Temp and Boost Pressure, Depentent on Vacuum

Function of Temperature- and Boost Pressure - Dependent Vacuum Control

On Engine 602.96

Function

When the engine is running, full vacuum exists at the central connection (VAC) of the pressure amplifier and controlled vacuum exists at the connection (VCV).

Coolant temperature <50 °C:
The automatic transmission pressure amplifier switchover valve (Y29) is connected to ground via a temperature switch; the valve operates the 2 - 3 connection.

Controlled vacuum exists upstream of the vacuum control valve at the connections (PRE and VCV) and acts against the vacuum at connection (VAC). This results in the vacuum required for transmission control at connection (TRA).

Coolant temperature >50 °C:
The ground connection at the automatic transmission pressure amplifier switchover valve (Y29) is interrupted; the valve switches 1 - 3. The connection (PRE) is now linked with the boost pressure line of the exhaust gas turbocharger. Once boost pressure commences, this acts against the controlled vacuum from the vacuum control valve. This results in a lowering of the vacuum at the connection (TRA) and thus in an increase in modulating pressure via the vacuum unit at the automatic transmission.


Modified vacuum control for modulating pressure effective 09/89

The temperature-dependent transmission control by the 50° temperature switch (S25/6) and the automatic transmission pressure amplifier switchover valve (Y29) no longer applies. As a result of this modification, the boost pressure influence is already effective at the pressure amplifier when the engine is cold. The transmission cold comfort circuit is controlled by a measure in the control valve body.
















Additional idle throttle switch for Improving gear8 shift if accelerator released rapidly

(deceleration upshift).

A second microswitch is fitted to the accelerator control at the engine end and a modified control cam to the accelerator control lever. In the idle throttle position, the microswitch (S27) switches the engine overload protection switchover valve (S66) to ground.

Air is admitted to the pressure line from the aneroid compensator unit to the pressure amplifier (PRE connection) via the engine overload protection valve. This produces a reduction in modulating pressure via the vacuum unit on the automatic transmission.

Electrical wiring diagram of temperature and boost pressure-dependent transmission control

Vehicle With Air Conditioning






625/6 50 °C temperature switch

S27 Microswitch, compressor cutoff/boost pressure cutoff

627/7 Microswitch, boost pressure cutoff

S66 Engine overload protection switch

Y29 Automatic transmission pressure amplifier switchover valve

Y30 Engine overload protection switchover valve

a Engine speed sensor, then coupling U of CE contact 6

b Kickdown cutoff relay (N15) contact 1

c Control unit (N6) contact 4

d Control unit (N6) contact 1



Vehicle Without Air Conditioning






S25/6 50 °C temperature switch

S27/7 Boost pressure cutoff microswitch

S66 Engine overload protection switch

Y29 Automatic transmission pressure amplifier switchover valve

Y30 Engine overload protection switchover valve

a Engine speed sensor, then coupling U of CE, contact 6

b Kickdown cutoff relay (N15) contact 1