Heater woes.

[tobyd]

Hi all,

Can anyone help desipher what is wrong with my 500E's heater.

The heater only ever blows hot (not warm) air into the cabin until the temp selector is set to minimum and then we can get aircon cold air.

The other symptom is while the engine turns over at less than 1500rpm or while idling at lights, the warm air stops after a few seconds and then cool air until i get moving or rev the engine, then warm air arrives again.

This is a pain at this time of year so I'd be grateful to anyone who wishes to share their knowledge with me.

Many thanks



Toby.

 

[landover]

Try bleeding the system .It may have an airlock.

 

[jberks]

Something to do with the thermostatically controlled duovalve, ambient temp fan/sensor etc ?. Sounds like its either on or off with nothing in between, so I'd go for the temp control stuff. It may the current drops at idle and shuts off the valve.

 

[sixpack]

cold heater at idle

HiAll,

Dont have a 500E but my C250 diesel does the same thing (heater goes cold after 30 secs idle). Tried searching for something I read a while ago about an auxilliary water pump. Didnt find anything, but looking at the cooling system, I found what could be an electric pump. On the C250 its on the inner arch, drivers side (UK car RHD), & its piped to the common side of the duovalve. Its possible its meant to start running at idle to give better flow. Its not the weather to do any more about it till spring, but I mean to replace all the hoses then as a precaution as they all look original, 220.000 mls on 1995 car. Will look at the "pump" then.

Hope this helps

Peter

 

[jberks]

Hi,
I believe this pump is for the auxiliary heater system- press the recirculate button when the engine is off and this should fire up, to keep the heater matrix supplied with hot water when the engine is off (until the block cools down).
So, it won't be anything to do with a cold heater I'm afraid.

 

[sixpack]

heater

Hi jb,

Thanks for your comments, but my C250 doesnt have aircon, so the recirc. function only refers to air circulation. The Haynes book doesnt show an extra pump for cooling, but they often miss things. Just to check I had my facts right I was going to try waiting for the heater to go cold at idle, then press the recirc button. I tried it today & the heater stayed hot !, Will try again tomorrow!.

Regards Peter

 

[jberks]

Hi Peter,
I have the same pump on my 210. Tube shape loosley rubber mounted on the O/S chassis rail with 3 pipes on it. I suppose it could fire up at other times but there isn't any technical advantage over just fitting a bigger pump (load would just be on the alternator instead of the water pump so no gain), so I doubt Merc would follow this route, they would just make the standard pump heavy enough to supply the matrix at idle. I don't think that you have to have aircon to have this feature though my '95 C doesn't have a residual heater or aircon and my aunt's '99 C has both so I suspect they added the feature during the '98 facelift. Also, I don't have this pump on my C and the heater remains toasty at idle, despite being a smaller engine so I still suspect you have a different problem.
cheers,
Julian

 

[tobyd]

Hi,

I didn't manage to get the heater in my 1992 500E fixed last year so I'm starting again. I have priced the parts that have been suggested but
before I get them I'm getting a mechanic to have a check of things. The symptoms are confusing.
All the info below was done at tickover in 17 degree outside temp, max blower and ec pressed unless otherwise stated.

The auxiliary water pump seems to run from start up (a bit noisily) and then not when the engine warms up. When the temp wheel was set to max the pump ran and stopped when not on max. The pump didn't run when on max after the engine warmed (the monovalve was vvv hot all the time).
The air only got hot when the engine was revvd and stayed hot whatever I did with the wheel until I engaged the aircon with the wheel on min then the air was chilled.

When i then turned the dial to the red zone the air redirected to the side and footwell vents and goes a bit warmer.When the engine is revvd the air gets hot and stays hot (aux. pump still). When I then turn the dial to the blue the air stays warm(not hot) and the air redirects to the centre vents. The air then stays warm until the aircon is activated and then it goes chilled.

Using the auto setting from cold air and turning to red/max the air stayed cold until the engine is revvd and then warm/hot air comes from side vents.
When the dial is turned down to start of blue, cool air comes from the centre vents but hot comes from the side vents - when the up/down aircon is activated the centre vents get cold but the sides stay hot (when 'nomal' aircon button pressed side vents get vvv hot). Hot side vents seem only to stop hot when the engine is stopped and restarted.

I hope this means something to those far more knowledgable than I and they can help me out (and my mechanic as climate control isn't that common in europe).

Thanks for your time.

Toby.

 

[paulcallender]

I am amazed you never solved this problem. It is due to faulty heater controls. Unlike other cars which have controls which attach with cables or levers, to valves, the W124 has a rheostat control, which drives valves electrically. I think if you clean the rheostats (variable resistor), or replace them, this would solve your issue. If it works can I have a go of your car LOL???

 

[tobyd]

Thanks for your help Paul. I'll let you know about the drive when the heaters fixed!