w123 heating issue - PeachParts Mercedes-Benz Forum

Ya Mar · #1 03-21-2011, 05:15 PM

Hello Everyone,

My '85 w123 300D Euro Import is having a heating problem.

The two center vents blow the SAME temp air as outside, never warm air.

The one vent for the driver and the second vent for the passenger blow slightly warmer than outside temperate air. They will blow mildly warm air if the car has warmed up for a long time.

Presently, the car can't really get warm because of the cold air from the center vents and only mild air from the other two vents.

What gives?

Thermostat?
Heater circulation pump?
heater control valve?

Hoping to get some ideas of what I may need to fix or adjust since it's too cold to drive the car without heat.

Thanks!

moon161 · #2 03-21-2011, 06:37 PM

Is it manual hvac (knobs) or klima (push button)? I have experience w/ the manual. Same or similar heater box, but klima is a beastly array of wires and vacuum hoses, manual is 2 knobs & 1 3 speed switch & defrost wire, and right & left up/down flaps & wires.

Heater core may be clogged or air bound. Maybe try disconnecting the 3 hoses to the heater core and flushing it. Note, water mains are 40-60 psi, auto cooling system design pressure is 15-20 psi. Be Careful, don't pop anything, like a 30 year old heater core.

Push/pull wires to the heater control valve may be jacked. See if the HCV moves freely, and if the wires move freely as well.

Center is fresh air vent, on manual hvac, there is a slider you can move to close it.

Otherwise, put a sweater on & warm socks. Boots w/ room let the blood circulate in your feet, long underwear is good if it's <20F. It'll be May before you know it, as long as you can keep the windshield clear, you'll be fine.

Yak · #3 03-21-2011, 07:07 PM

Quote:

Originally Posted by Ya Mar

Hello Everyone,

My '85 w123 300D Euro Import is having a heating problem.

The two center vents blow the SAME temp air as outside, never warm air.

The one vent for the driver and the second vent for the passenger blow slightly warmer than outside temperate air. They will blow mildly warm air if the car has warmed up for a long time.

Presently, the car can't really get warm because of the cold air from the center vents and only mild air from the other two vents.

What gives?

Thermostat?
Heater circulation pump?
heater control valve?

Hoping to get some ideas of what I may need to fix or adjust since it's too cold to drive the car without heat.

Thanks!

I thought on the Euro's the center vents were only "fresh air". As moon indicated there ought to be a slider to adjust the quantity of fresh air.

Regarding the lack of heat from the other vents or for the floor, it could be a few problems.

More info would be helpful: what does the temp gauge read? Is the car warming properly? If not, then maybe there's a thermostat problem? Or maybe somebody wired the aux fan to run all the time.

What kind of HVAC or ACC system? Pics would help.

What other troubleshooting have you tried?

MBeige · #4 03-21-2011, 08:33 PM

This might help

Ya Mar · #5 03-21-2011, 11:04 PM

Hello All,

To answer the questions:
1) The center vents have a slider, but it doesn't seem to do anything...maybe the flap the slider controls is broken...? I'll have to look into that separately so I can prevent fresh (cold) air from coming in when I don't want it.

2) The HVAC is the manual Euro style with the 2 temperature knobs and the fan speed knob. It seems that regardless of the temperature knobs position it blows mildly warm air. Not cold, not Hot.

3) The car doesn't run very warm, in fact, it may be running on the cold side, usually below 80C? I'm not sure what the average running temp is when it's warmed up.

I have an extra thermostat I could install, but I'm not sure if that's the problem. It does seem like there are some issues with the temp knobs on the HVAC unit itself.

Any thoughts?

Ya Mar · #6 03-24-2011, 10:42 AM

Does anyone know how to get access to adjust the flap for the center vents?

I think if I'm able to close those vents it will help a lot.

I don't want to start taking the dash apart unless I know where the flap is.

Thanks everyone!

Stretch · #7 03-24-2011, 10:50 AM

You can probably reach the flap control lever inside the cabin by gaining access behind the middle console: grope about in the foot wells and you'll probably be able to reach it from there. It might prove to be easier to remove the glove compartment and get to it from there.

To see the flap itself you can access it from the outside of the car. You need to remove the cowl grills just behind the bonnet / hood and then gain access to the area under the steel plate that covers the windscreen wiper motor.

EDIT:-

If you want to see pictures of the area under the cowl grills have a look here

A happy I found no (well hardly any) rust on my W123 thread!

moon161 · #8 03-24-2011, 11:53 AM

The slider/oav is a neat little mechanism, you may be able to access it if you pull the glove box or cluster. It took a while to get at it the first time. It's really best if you show a picture of it to your capuchin monkey and send him in after it.

I'll take a look and cogitate on it over lunch.

Sounds like your tstat has failed open. If the Tstat's OK and it's extra cold, you may need a Molson or Labatt front.

Ya Mar · #9 03-24-2011, 06:12 PM

Hello,

I was able to reach behind the dash from the passenger foot well and I could feel the slider and I could feel the long lever that the slider was SUPPOSED to be attached to. I reattached them and now the slider opens and closers the center vents.

This makes a huge difference in getting the car warm.

I will keep an eye on the running temperatures and the temp of the heat from the heat and decide whether or not the tstat needs to be replaced. I did get a spare one so I could replace it.