testing switchover valves for 300D/123
 

Quick question,

On w123/300D's the switchover valve on the firewall is plugged/blanked off at the top vacuum valve (which is normal on most w123s).

The other two openings go to the banjo bolt and ALDA. According to search results, people say you can blow through it with the valve unplugged.

But what about when it is plugged? One of the leads gets juice. Should I be able to blow through the valve when its plugged in?

Connecting the electrical plug won't make any difference, unless you also provide a ground. In normal operation, the circuit is open. When an overpressure condition exists in the intake manifold, the switch there closes to provide a ground and causes the switchover valve to actuate.

Hi Tango,

Thanks for the reply. So if I were to hook the switchover valve directly to a battery, I should NOT be able to blow through the valve? Or I should be able to hold a vacuum on both nipples? (same thing I suppose). Thanks.

If you complete the circuit, you would not be able to blow through the normal two ports, one would be blocked and the other would blow through the top.