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  #1  
Old 06-11-2019, 11:28 PM
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Why did they choose such a poor design for the mono valve?

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.
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Old 06-11-2019, 11:51 PM
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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.
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Old 06-12-2019, 06:42 AM
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Quote:
Originally Posted by Diseasel300 View Post
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.

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.
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Old 06-12-2019, 07:31 AM
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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
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Old 06-12-2019, 11:18 AM
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Originally Posted by 97 SL320 View Post
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.
Do you have a picture of where you put the ball valve?

Last edited by gregp1962; 06-12-2019 at 11:35 AM.
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Old 06-12-2019, 12:23 PM
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Quote:
Originally Posted by Diseasel300 View Post
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.
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.
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Old 06-12-2019, 12:29 PM
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Quote:
Originally Posted by gregp1962 View Post
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.
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Old 06-12-2019, 12:32 PM
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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.
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Old 06-12-2019, 12:35 PM
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Originally Posted by BWhitmore View Post
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.
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Old 06-12-2019, 01:08 PM
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Quote:
Originally Posted by oldsinner111 View Post
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
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...
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Old 06-12-2019, 01:35 PM
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Quote:
Originally Posted by oldsinner111 View Post
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
Quote:
Originally Posted by vstech View Post
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...

First, a post that had nothing to do with this thread, and then a response to the nothing!!!
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Old 06-12-2019, 01:44 PM
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Originally Posted by Frank Reiner View Post
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!
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  #13  
Old 06-12-2019, 03:59 PM
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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.
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  #14  
Old 06-12-2019, 04:06 PM
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I believe this post transitioned into a discussion about home HVAC.
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  #15  
Old 06-12-2019, 04:46 PM
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To get back on track, what type/size of ball valve would do the trick in this application?
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