zsjad

Dear members
I have a 1993 230E in South Africa and in prestine condition with only one problem, namely that with the temperature control wheels in the cold position, hot air still flows into the cabin
I tried to search, but I am either too stupid to find threads or posts or nobody else has ever had such a problem, which I find difficult to believe
I suspect that the problem is with the HVAC heater control valve, also called duo valve or some rheostat perhaps under the dashboard
Can somebody please direct me to threads or walk me through a process of checking where the problem lies
Your assistance will be highly appreciated
Kind regards
Johan Louw ( Logged in as zsjad )

Plutoe

Dear Amazed, first take the car to any AC shop, preferably not a family member, and ask to have a set of gauges put on the car, what is the H and what is the L pressure and did any one indicate that the refrig is low or what was the expression on their face?

teahead

May have nothing to do w/AC.

I don't have those type of controls (auto type), but are you saying whether the AC button is on or off, heat is coming out of the vents as if the dials were set to the HOT position?

zsjad

Sorry guys for the long delay, but yes, I confirm that hot air is entering the cabin with the thumbwheels in the cold position
To my mind it means that the hot water is never cut off from flowing to the heater core under the dash or wiper motor. I believe it is supposed to be done by the valve mentioned in my first post. I can't however not work out how this valve works. When I put 12 volts on the valve its electrical motor spins
Any advice out there will be appreciated

Floobydust

The valve you are referring is either a mono-valve or a duo-valve depending on the type of HAVC system you have in your car. If you have two temperature thumb wheels you have a duo-valve and if only one, you have a mono-valve. The valve assembly also contains an electric circulation pump to boost hot water flow. This is the motor you hear running. These vales are somewhat unique in that when they fail, they fail open thus causing hot air to blow all the time like what you are experiencing. There are two electrical connections to a mono-valve assembly - one for the pump motor and one for the valve itself. If you have a voltmeter, check for 12 volts on the valve connector (not the motor connector) with the temperature wheel set at cold. If you have 12 volts, the valve is bad; if you don't there is something wrong with the climate control unit. The CCUs are pretty robust, so I would bet on a bad valve.

zsjad

Thanks Floobydust. Your reply is the exact start to my enquiry that I was hoping for and I think you have got it exactly right. Is there anything one can do to repair such a valve? I believe they are scarce and costly
Kind regards