Simple Question - PeachParts Mercedes-Benz Forum

psaboic · #1 01-10-2020, 09:59 AM

At least I hope it is. Anyway during cold weather when I used to start the 83 300D up first thing in the morning, I could press the defrost or any other button on the climate control and I would get slightly warm heat right away that would gradually get warmer as the motor warmed up. Now, I don't get that heat until a few minutes have passed and the motor starts to warm up.

I used to remember what might cause this, but for the life of me, I cannot remember now. Any tips on how to troubleshoot and fix?

Thanks

Diseasel300 · #2 01-10-2020, 10:44 AM

If the engine is stone-cold, the heater core will be the same temperature. You won't get any heat until the engine temperature is several degrees above ambient temperature. It can take several minutes.

If you're plugging in the block heater overnight, you should have a lukewarm water jacket. If that's the case and you're still doing it, the block heater probably died.

psaboic · #3 01-11-2020, 01:03 AM

Yes it was a stone cold engine, and no I have not used the block heater in 3-4 years.....

barry12345 · #4 01-11-2020, 04:34 AM

If you do not have it started yet. Sitting a long time possibly will require the glow plugs working properly. Even at 60 degrees.

rocky raccoon · #5 01-11-2020, 07:58 AM

You car has a small electrical auxiliary coolant pump located on the inner front fender on the passenger side. The purpose of that pump is to circulate coolant through the heating system when idling or driving at slow speed. It is intended to operate as soon as the car starts and when heat is selected at the pushbutton control unit. The is the source of the "instant" heat you were getting.

Check that the electrical plug is firmly attached and if you have the capability, check for voltage at that plug with engine running and heat selected. Also check operation of the motor by feel. It is all very easily accessible. Look straight down to that inner fender. The motor is about 2" in diameter and mounted in a rubber vibration isolator.

If the motor is bad, unfortunately new ones are vastly overpriced. Look in breaker yards for a replacement or just bypass it with a piece of hose as many of us done. I don't miss mine at all but I don't spend a lot of time idling in traffic.

Please come back and let us know how you do. It will help others.

ykobayashi · #6 01-11-2020, 08:08 AM

Is your blower turning on?

Or are you saying no heat comes out? If your engine is stone cold you won’t get any heat. The water needs to warm up and the thermostat needs to open. Then the monovalve has to open.

I had a little problem with the blower not coming on after I got the car warmed up. It turned out to be a temperature switch on the thermostat housing that signals the climate controller to turn on the fan. I could override it by hitting defrost but not by hitting EC. I think this was done so you could clear your window if it started fogging up if you needed to immediately get under way.

Check this sensor and check the wire. My wife was snapped. This was on my 85 300d California.

Blower not turning on with EC button CCU/Programa works with DEF SOLVED

psaboic · #7 01-11-2020, 11:20 AM

Thank you Rocky, that is the answer I was looking for. I thought there was an aux pump as I remember adding a fuse to the circuit many years ago, I just couldn't remember its exact function. I will check it as soon as I can (may be a few days) as they are predicting snow and near gale force winds here the next several days!