Mercedes-benz w124 heater valve replacement 1986-1995 e-class pelican parts diy maintenance article electricity notes pdf


If you are having trouble with your climate control system on your W124 from no heat to heat all the time, one of the issues can be the heater valves. The heater valves allow hot coolant from the engine to circulate through the heater core and warm the HVAC system. If you are only getting cool air from your system even with the heat turned to MAX, or you get nothing but hot air all the time you may have a faulty heat valve. One of the ways to check is to carefully place your hands on the heater core hoses to tell if warm coolant is flowing through them while the heat is turned on. Use care as the coolant and hoses can get very hot.

This article will show you how to replace a faulty heater valve. Begin by working on a cool car. You will be working with the coolant and do not want to burn yourself. You do not need to drain the entire cooling system. If you are replacing the very expensive heater valve now might be a good time to give it a good flush. Please see our article on flushing and replacing your coolant.

Comments: 94 Mercedes E320 W124 the heater seems to be stuck on full heat. Temperature control does not change heat output -100% heat. By unplugging and plugging back the short valve I can hear the click so assume its working and the taller valve which see like a pump also seems to be running when call for heat. Anyway wonder if I need to replace the heater control valve – a lot of money to spend if I’m wrong. Any help would be appreciated. Thanks

Can i bypass the heater valve and connect the hoses directly to the heater core to always allow the coolant to enter the heater core during its normal circulation? Does doing this will help engine cooling as its heat reaches 105C when AC cooling is on when idle in slow motion and on heavy traffic ?

Followup from the Pelican Staff: it can cause you A/C to not cool as well, with the added heat in the heater housing. I would suggest checking if the radiator is restricted (is it cooling correctly), the system should be able to maintain temps for you. – Nick at Pelican Parts

Comments: Hey there, I wasn’t getting any heat to my system with the temperature turned fully up and the fans on max in my 1991 300ce. I tested the heater valve and found it to be faulty, so I used your instructions to change out my heater control valve with a newly tested replacement. Thanks to your article it went smoothly. However, after installing the new heater control valve I still wasn’t getting any heat. The new valve tested good but still no heat at normal operating tempertures, just cold air. The hoses running to the valve from the water pump/engine are hot, the two hoses from the valve are hot, but right before the one hose connects to what I believe is the metal heater core line going into the cabin, it gets cool like the coolant is not running any further. Does this sound familiar to anyone and can someone point me in the right direction. Thank you sooo much for these tech articles.

Comments: My pleasure. I don’t know if you can answer this but I have a question about that valve. I am planning to do a thorough flush of the coolant system. Rather than running everything through the block and radiator drain. I would like to flush the heating system directly running water from the driver side line to the heater core and detaching the hose on the heater return line under that heater valve. The question – does the flow from the windshield washer heater through the valve stay open at all times? If not, will it open if the heater is on? Thank you!