Very little heat in W124

[kps70]

Hi - my first post!
I have recently bought a 200TE (no air con) and it's great apart from one thing - very little heat from the heater.
The fan is working fine but the air comes out cold on the passenger side and just slightly warm on the driver's side but not enough to warm up the car. It seems that the temp dials have no effect on the heat. Also, clicking the dial onto the window/demist setting (presume this means 'on' all the time?) seems to have no effect.
Is there some sort of checklist I can work through?
I hope you can help!
Cheers
Kieron

 

[Will]

Hi there and welcome

What temperature is the car running at on the dash - should be around 85-90c.

If it was running a little on the cool side (eg thermostat sticking open etc) then the heater core will be running too cool to provide adequate heat.

It might also be worth checking the 'duo valves' if fitted to your model - they're normally located near the brake master cylinder and control the flow of coolant in the heater IIRC.

Will

 

[vincenz]

If the dials don't appear to be working it could be the a connection that controls them has come loose.

Following http://www.mbclub.co.uk/forums/interior/61201-how-change-w124-temperature-dial-bulbs.html to get to the controller and there is a rectangular connector that should click into the dial housing.

 

[grober]

There is a small electrical circulating pump close to the duo valve assembly which is in front of the brake servo unit. It might not be working? The fact that you have difficulty switching flows in the heater might point towards a failure of the vacuum system. the heater flaps on these cars are operated by vacuum derived from the engine manifold. If the vacuum supply has failed or one of the vacuum diaphram actuators has failed then the system stops operating. deffo worth checking the vacuum system.

 

[kps70]

Thanks guys, I'll check the things you've listed for me and get back to you.
Kieron

 

[kps70]

I've checked the thermostat and yes it was stuck and running cold. However, after flushing through the system and replacing the thermostat, there is still no heat. Next step, vacuum system?

 

[goldestate]

As WILL says Try carefully cleaning duo valves I am sure there is a listing with pictures somewhere it won't do any harm anyway you can consider it maintenance its easy and cheap!