190E Vac Line Behind Battery Box - PeachParts Mercedes-Benz Forum

E.J. Kubatko · #1 08-11-2004, 04:17 PM

Immediatley behind the battery (just behind the flimsy plastic firewall shield) I see what I think may be a vac switch (?) mounted vertically on a metal bracket that's parallel with the dash. There are wires running to it and, what appears to be, a plastic vac line male insert stub projecting from this little black device. Mine has no vac line connected to it. Should it? And if so, what does this thing control and from where does the vac line come? Any help will be greatly appreciated since I'm troubleshooting. I have a '92 2.3.

mbdoc · #2 08-11-2004, 05:44 PM

That is the atmospheric pressure sensor for the fuel system. No vacuum line

E.J. Kubatko · #3 08-11-2004, 07:10 PM

Thanks much, Doc. I'm trying to chase down a vac leak (I assume), which is causing heat to the side vents. I checked out all the usual suspects -- connections by the fuse box, vac switchover block, line to heat valve, lines to vac reservoir and reservoir itself. Is the entire vac system interconnected? If so, any ideas on where else I can look? The problem is not major because heat only begins to be discharged from the side vents while engine is under load -- like up long grades -- then after leveling out the heat stops. Could this be symptomatic of a bad heat valve?

mbdoc · #4 08-12-2004, 08:10 AM

The heat from the side vents is a sign of a VACUUM leak. The heater valve is vacuum closed. Most common problem is the fresh air vacuum diaphram & the blend air diaphram. You need hand vacuum pump to check for leaks. The system need at least 10" of vacuum to operate. There is a vacuum storage tank under the right front fender near the battery, possibly the vacuum line there has been damaged by battery acid.

E.J. Kubatko · #5 08-14-2004, 08:11 AM

Re: My previous post regarding unwanted heat from side vents

With thanks to M.B. Doc I solved my problem by using a free-rent hand vac pump from AutoZone to test my vac lines. After checking 4 or 5 lines that tested ok by holding 12" of vacuum, I discovered that the green line (w/red stripe) -- going thru the firewall abv fuse box to switchover block -- would bleed down quickly. Problem was a leak at the L-shaped rubber connection to the switchover block.