1981 to 1984 W123 Klima Heater Control Monovalve Conversion w/ Free Performance Upgrade Kit

For late W123 with the ACCIII automatic climate control. Will not fit 1985 models with trap oxidizer. Limited stock.

 Are you tired of your sluggish heater system? Does it take too long to change temperature. Does it get hot when you want it to get cold. The old original Bosch monovalve is no longer available new and it really has outlived its usefulness anyway. This is probably the very best upgrade you can make for your automatic climate control. It will switch the hot to cold or cold to hot much faster and will hold a much steadier heat at high engine speeds. The original heater valves are old and they are tired. Even the newest model is now 30 years old. If you own one of these cars, you might agree that your systems “works” most of the time but sometimes, not so good. In the past, you probably replaced the mono valve and things improved. At least you were getting hot when you wanted it and could turn it off when you desired. But now you find out that Bosch is no longer making the mono valve replacement and your system is acting up again. This valve is the HEART of the system. If it is damaged or not working properly then you will never get the heater to work right. Bosch monovalves and monovalve repair kits are now no longer available new. Many aftermarket rebuild kits are notorious for poor quality. Even after rebuilding, the OE Bosch monovalves tend to operate poorly at high RPMs and are prone to sticking. Klima Design Works BV Series valves are a new and superior replacement heater control valve system that uses technology from late-model vehicles.

1981 to 1984 W123 Klima Heater Control Monovalve Conversion w/ Free Performance Upgrade Kit
Free Add-Ons Included:

How to Install our ACCIII Climate Control Performance Upgrade - On Demand Video

How to Install the Klima Heater Control Valve in the late W123 and the 380SL - On Demand Video

Product Details

watch road test results

We include a bonus kit that will increase the longevity and performance of your system. Many don't realize there is a rotten deteriorated foam hose that has fallen off your center dash temperature sensor thus making the sensor "confused." Many also do not realize an overloaded aux. water pump can damage your climate control panel. Many don't realize the aux. water pump is not even working and can lead to poor heater performance. (It is better to remove it all together than to leave it installed when it won't pump! You will receive a replacement hose and fuse with complete video instructions.

WARNING: Keep in mind this valve may not fix all your heater issues. You must also have the following:

  • 1. A good working auxiliary electric water pump ( replace or remove it from the system at best )
  • 2. Non deteriorated temperature sensor foam hose under your dash ( replace it with our kit)
  • 3. Good working heater blower motor
  • 4. Properly functioning climate control push-button panel
  • 5. Properly functioning temperature logic box ( located under dash behind glove box)

It may take some work on your part to troubleshoot additional problems with your system. Since it is the “heart” of the system replacing the monovalve is the best place to start. It is almost impossible to troubleshoot other problems unless you first know you have a good working valve assembly. 

Here is a picture of the valve installed in a 1984 W123 300D:

If you want the best way to test your current monovalve or electrical water pump get our 12 volt power probe tester. See related products below:

We highly recommend you replace your old Bosch electric coolant pump with the newer Bosch pump used in many of the 1990 and early 2000 models. This pump will increase the reliability and performance of your climate control system. We offer a complete conversion kit. See the related products below:


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