My A/C works great. But, if I turn off the car even for a second, the A/C blows hot for a few minutes afterwards. Obviously, it's letting hot water into the core when the engine is turned off. It is a rather new mono valve. But, an adequately designed valve wouldn't do this even when it is malfunctioning.

When the car is switched off, the monovalve is disengaged. Remember, it engages to close off water flow, so for the heater flow to be off, the monovalve is powered. If your A/C is working even halfway properly, it should be able to overcome the heater core heat within a few seconds. If it's taking it minutes to start blowing cool again, you have bigger problems. Make sure your recirculation door is closing.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

This is why I add a ball valve to the heater inlet side of the heater core. ( the mono valve is on the outlet on my 97 SL and C ) This helps even when you are not using the AC.

like to add something,for heat pump user's for home.Some people get high bills in summer,as heat strips try and run,at same time.I disconnected emer. heat with,and used a micro switch.Saves money in winter,when not to cold

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

Do you have a picture of where you put the ball valve?

The AC is working great. Very cold. But, when even a little bit of very hot water gets in the heater core, there is no way that a good AC is going to cool that down is just a few seconds. The problem is that this poorly engineered valve shouldn't allow even a drop of hot water into the core just because it was switched off for a few seconds or minutes.

I dont think you can overcome laws of physics. When the valve is de-energized the coolant path is open, as the core is cooler than the engine, hot coolant will flow to it just by convection alone.

As SL320 mentioned - installing a ball valve can help or an oldschool heater valve from a car that used mechanical operation.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

The ball valve should be installed in the heater hose leading to the heater core. I would think that valve should be closed during times of the year when you know no heat will be required.

I have seen a lot of old Brass type valves installed on old mercedes and BMW in other countries where its hotter than the sun itself.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

The strips certainly shouldn't be engaging when in ac mode...
Either your strips are damaged and shorting to ground, or the controller is failed... thermostat issue etc...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

First, a post that had nothing to do with this thread, and then a response to the nothing!!!

And then a response to the response to the nothing!

__________________
Stop paying for animal enslavement, cruelty, and slaughter. Save your health and the planet. Go vegan! I did 18 years ago. https://challenge22.com/

DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

oldsinner and vstech, I'm not sure what you two are talking about. This thread was talking about how the mono valves are poorly engineered.

I believe this post transitioned into a discussion about home HVAC.

To get back on track, what type/size of ball valve would do the trick in this application?

__________________
1991 300D 2.5 "Rocinante"
2002 Golf TDI "Teen Spirit"
--------------------
1984 300D
1966 Mustang I6 3sp
1985 Mazda RX-7 GSLSE
1982 Toyota Supra
1977 Datsun 280z
1971 Datsun 240z