I have a problem that the AC unit will blow hot air when both temperature controls are set to full cool. Looking around the forum it was suggested that the duo-valves were stuck.
https://www.crossfireforum.org/forum...ggestions.html

So what does the duo-valves have to do with the AC? Looing at the ducting for the HVAC system, it's important to understand the airflow. Looking below at the diagram the heater core is before the AC core. That means the hot air is blown through the AC core. In a way the heat will take precedent over cool this is very helpful when defrosting the car where you want to heat and extract moisture out of the air.


HVAC ducting and routing


Of course looking in the manual you can't find anything called duo-valves. I eventually found what is the proper name: Coolant circulation valve.

Coolant Circulation Valve

So what is the Coolant Circulation Valve? Look at number six in the below diagram. Coolant refers to the engine coolant to cool the engine. When it's run through the cabin heater core, it's actually hot water. There are two valves that allow water to flow through the heater core for the cabin air. Since the heat can be controlled for the passenger and driver there are two valves.


Hot water circuit for engine coolant

The unit has two solenoids and two valves that can wear or get stuck. If you have the AC pump turned off and the temperature selectors turn to full cool and the hot air comes out of the system, the the coolant circulation valve needs maintenance. You can buy a rebuild kit for the unit off of amazon.

Rebuilding the unit is easy. Pull the electrical wire. Open the antifreeze reservoir cap to release the system pressure. Use a splined screwdriver to remove the five screws.

The Duo-valve or coolant circulation valve

You can just pull the top.


No top with valves down in their seats

Here is a picture showing a worn valve.

valve

Use the kit and remove the oval seal. Clean all surfaces. replace the valves back into the seats. Carefully align the solenoid shafts onto the valves and place down. Tighten all the screws. Put the wiring back and test. If that does not work. Then the solenoids are bad and the unit will need replacement. Here is the instructions on removing the unit.


removal instructions

 

Nice write up.

 

Great write-up and visual aids! Just one clarification, it isn't hot water. It is the cooling system coolant that circulates through the two section heater core.


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Thanks for the write up xintersecty!

 

Good write up, but two things:
If one or both sides are stuck OR if there is no 12 volt feed to the center pin (I had that once), you will get hot air if the engine is warmed up, having the A/C pump on or off won't matter, because the coolant temperature will be at least 188F - and the air flows thru the heater core(s) after being cooled by the evaporator.

Quote:

Of course looking in the manual you can't find anything called duo-valves. I eventually found what is the proper name: Coolant circulation valve.

Chrysler calls it that, Mercedes calls it a duovalve because there are two valves in the assembly.

 

Here are some electrical specs to help you know more about these valves. The electrical fail point is this 22ohm MOV (metal oxide varistor) that energizes the solenoid.

 

Here are some electrical specs to help you know more about these valves. The electrical fail point is this 22ohm MOV (metal oxide varistor) that energizes the solenoid.

 

So I'm confused....I have a 05 Chrysler Crossfire base and mine looks nothing like what u just posted....am I missing something..? Tks!


Disregard, had to pull the rest of the unit up...lol

 

I was editing the picture when you modified your post.

The valve is under the black part

Top part of the valves is the solenoid that controls the valve. the black cylinder is the guide pin going to the brass wedge shaped valve. More pictures the better.

 

I do have a question..my valves are solid copper like, not plastic and they don't have a oring going around them. The only parts i could use is the flat 2 hole seal and the replacement cooper valves. I had a additional 2 o-rings and 2 other round rubber seals and 1 large o-ring. What do those go to? Thank you!!

 

[QUOTE=Bzak1pgh;993095]I do have a question..my valves are solid copper like, not plastic and they don't have a oring going around them. The only parts i could use is the flat 2 hole seal and the replacement cooper valves. I had a additional 2 o-rings and 2 other round rubber seals and 1 large o-ring. What do those go to? Thank you!![/QUOTE

The parts that need replacing, are the valve seats, brass valves, and the gasket.


Mercedes Duo valve rebuild kit

 

Yeah, I didn't use the vavle seats, couldn't get them out, I was afraid of breaking something... but after replacing the valves and the gasket, worked great. My gasket was literally melted in that silver plate!! I had to use a rotary wire brush to get most off

 

I don't think I replaced the valve seats in mine too. Come to think about it, I don't think I got them.

 

My original issue was hot air on DS; PS was still getting cool air. When this happened to me, I found the attached Post that describes a 'flushing' procedure that sometimes restores HVAC performance. After I did this, my HVAC system worked fine & is still working. I probably will need to repair the Duo-Valve one of these days, but I'll wait until that time comes around.

 

2006 Base Roadster, manual transmission.
Hi all,
I plan on doing the hvac duo valve repair, I'm waiting on the parts. I'm getting warm air blowing constantly. I can get cool air if I put the A/C on high and using the REST button.
I've also noticed that the fan speed does not adjust properly. I've just recently replaced the blower motor resistor. I believe it may be the potentiometer that is causing the issue with adjusting the fan speed.
Example: I turn the **** to position 1 and it works at low speed but to get it to blow out at a higher speed I have to go to pos. 4. There is no difference in fan speed between 1 and 4.
I've heard that tapping the console will fix this, but that is only a temporary fix.

My questions are; Has anyone had this problem with fan speed adjustment? If so do you think it is the potentiometer? Also, is it a hard job to replace them? (I already have a few of them from Digi-Key, thanks to Mark's advice.)
Last question; The warm air blowing all of the time, could that also be the outside temperature sensor? When I first got the car if it was hot out cool air would blow in even with the controls off. If it was cold out warm air would blow in. Now it's constant warm air.
Thanks for any help in advance.

 

I just replaced mine, took 10 min. Fixed the issue. Mine is a 05 Base though...shouldn't be much difference.

 

Are you talking about the duo valve or the potentiometer? For the potentiometer you must disassemble the dash which takes longer than 10 minutes.

 

I'm going to try repairing the duo valve first.
However, I don't think that will solve the fan speed adjustment problem. I guess I'll have to do both.

 

Thus is what stopped my hot air blowing and what took about 10 mins.. sry for the confusion...lol

 

No problem. I appreciate your post, it is very helpful!