Testing for pluggage in 1985 300D heater core
 

I've got the car in that is kicking my butt in regards to making the heater work ( A/C blows cold:). Anyway, I've got a known good monovalve installed and even with the wire at the monovalve disconnected it still blows cold whether I am at idle or driving down the interstate. My next step is going to be to disconnect the hoses at the firewall and see if I can blow through the heater core. Any other things to consider while in there. tia

disconnect the hose to the top of the mono valve and pump back towards the fire wall.

disconnect the hose on the back of the head so that if there is anything in there it will flush out there instead of into the engine or radiator.

Is the heater core hard to get at on the w123? Just curious cause I know someone who has one that might be leaking.

Lol, I don't even want to have to think about replacing heater core. Not necessarily as much a pia as time consuming.

Well....you will have to remove the Dash, and Iam pretty sure you will have to remove the Heat/AC control box assy.

I have removed about 5 of these in the PNP yards, and it is a bit of work to do. The heater Core sits vertically facing the radio part of the dash panel. On the Firewall (eng side) you will see the 3 pipes the heater hoses connect to. These pipes are bolted to the Heater Core. So it isn`t something you can easily lift out. Plus you will have to discharge the AC Freon if there is any.

The Heat/AC control box assy. is three pieces with side clips that hold the case together, you have the AC Evaporator, Blower Motor, Heater Core, and vac lines etc...

As mentioned by Engatwork, time consuming.


I wish this was as easy and the one I just replaced on my 86 Ford F-250.
2 heater hoses on the Eng. side, drop the knee panel on pass side. and there she is looking at you. Easy R&R.

Charlie

Hmm
 

I will try to call this afternoon.

.

I've heard rumours of people removing the heater unit with the dash in place - getting at it from the passenger footwell...

...don't know if that was also with AC - if I remember correctly it wouldn't have been too hard to do that with my Euro non AC unit.

Still I'd be looking at the valves that open or close the flow first. (Again never seen an AC unit so I don't know how that works - my 300D has two little white plastic taps with cables that go into the cockpit - all very simple)

Have you checked your auxillary water pump to see if 12 volts makes it pump and its not plugged?

Have verified that all your vacuum pods are working? I had a issue in my 126 where the cold air from deforst would blow at same time as heat .
After replacing the pods including the main flap all air comes out where it is supposed to.

Just a thought.
greazzer2b

Thats what i thought looking at it. The last heater core i did was a geo prism 15 years ago. It was a 30 minute job and 20.00 part. I think i'd have to take a sawzall to the dash or firewall if this ever happens to my car. lol. That would be more fun.

Here is a couple pictures of the unit.
http://i58.tinypic.com/4hqyyx.jpg

Here is the heater box out, and one the driveway.

http://i57.tinypic.com/wsaip3.jpg

You can see the 3 aluminum pipes at the top of the picture, the core is behind the center vent opening.
That center panel needs to come off as I remember, so maybe the whole box does not need to be removed from the vehicle. Remove it and the core may be able to lift out.

And the heater Core.

http://www.peachparts.com/shopforum/..._exchanger.jpg


I borrowed these form a couple other threads.

Also daw_two has a good set of pictures:

How To Disassemble A W123 Manual Airbox Photos by daw_two | Photobucket

Charlie

working to hard
 

Disconnect the heater hoses.
Reverse flow through the heater core, full volume with a garden hose.

To clear the air vanes.
Blast two full cans of scrubbing bubbles through the air ducts.
Flush the duct work / heater box with massive volumes of water.
YES, the floor pan will flood, be prepared.

.

On list to do this today.

Thank goodness the heater core is fine.
 

I'll be dog gone. Something is going on at the other end of the engine. Upper radiator hose is hot and lower is cold so I will be getting into engine cooling system sometime today.

But upper hot lower cool (progressively on radiator) is normal. Laws of physics.