'84 300D A/C and Coolant issue
 

ok...this is not my car, so I can't really give you a lot of information.

When using the AC, after a while there is a coolant leak from the Y pipe mounted on the firewall and feeding the inside of the car.

A/C is not blowing all that cold, but I can't tell if it's cooling at all as it was evening when I was testing.

Here is what I suspect: With a low charge, the AC is freezing up the evaporator core inside. With this freezing up, the coolant is restricted causing back pressure and thus the high pressure leak around the seal.

Anyone think I'm completely nuts, or is this possible.

The problem ONLY occurs when the A/C is used.

The leak is from the bottom side of the Y connector.

Thanks in advance!

A 1984 300D.... ?
and there is another thread saying you are picking up a 1984 300D...
very suspicious....

Why do you think the AC is low on charge ?

With a low charge the AC should not even be coming on.
If it is coming on and then stops cooling then it can be the expansion valve failing to keep the evaporator above 32 degrees... if it gets below that then ice forms in the air flow path....making it feel like it is not cooling.

Have you checked that Flap which , if not closed, allows warm air to mix with the cold air, making it feel like the AC is not working ?

That ought to keep you busy a while....

Ok, here are some pictures.

in the first picture, the Red arrow shows where the coolant is leaking from. It supposedly comes out in a hard stream.

In the second picture, I have circled the "Y" pipe in blue. This Y pipe is connected to the hose coming off the manifold.

In the final picture the Yellow line points to where the water streams out, and the red arrow shows where the hose enters the firewall.

I believe that this may be due to icing up of the underdash parts which is causing the coolant to build up pressure and squirt out passed the hose clamp. I say this because when I had a problem with low coolant level once, I had a freezing problem.

Remember, I claimed ignorance of the way it worked, and I am giving you theories from that viewpoint....

Hope this helps.

You seem to be connecting engine coolant and AC refrigerant with regards to this.. ????
At what point do you see these interacting ?

I'm figuring they interact inside the car where the blower uses them to blow either hot or cold air....

The evaporator is not nearly close enough to the heater core and hoses to even come close to icing them. Also, when the monovalve is closed the pressure in those lines is as high as it ever gets anyway. The systems are essentially isolated from one another, at least from an energy point of view. (Air flow from flap positions doesn't count. ;))

When the A/C is on, the monovalve should be closed and that may be why the coolant leaks (pressure). Tighten the hose clamps or/and replace those heater hoses and I think that the leak part of the problem will be solved.

As for the A/C not cooling as well as you'd like; wouldn't hurt to check the monovalve diaphragm while you're there. If that's OK you can check the A/C, subsystem by subsystem; clutch, aux. fan, viscous fan, condensor clean, pressures, PBU, etc.

If you have coolant leaks, fix the leaks. They are not connected with the A/C.
If your A/C is not cooling, ensure that your heater is off. If you cannot turn the heater off (ACC issues?) check the temperature of the refrigerant from the compressor to the condensor, it should be hot. If so, check the refrigerant coming from the evaporator, it should get COLD.
If not, problems with A/C

Physics of climate control and engine cooling 101
 

Cooling system leaks become more notable during A/C operation because.
#1. Condenser heat transfer to radiator.
#2. Engine load.
#3. Reduced radiator heat rejection capacity = Lime buildup, corrosion or material breakdown from age.
#4. Bad thermostat.
#5. failing water pump.

Added heat = added pressure = weak points fail = a damp spot becomes a stream or spray. :eek:

Best advice: :)
#A. Replace the thermostat.
#B. Flush the cooling system.
#C. Disconnect, clean the leaking hose end and fitting, reconnect.
#D. Clean any trash from between radiator and condenser.
#F. Clean trash from under electric cooling fan, may need to remove fan for this.

Might be good to look at it backwards.... a leak means that the pressure can cross the threshold from just hot water to steam at a much lower temperature.... due to the lack of pressurization ...
Also need to check the Radiator Cap pressure.

When I get a "new" old Mercedes one of the first things I do is inspect all the hoses and clamps. I have found bad upper hoses due to rubbing on 2 cars. I have never found a bad heater hose, but I have found numerous hose clamps to be loose and leaking. From the looks of it, those are the original factory hose clamps, which means they probably haven't been tightened in 21 years.

Thanks Everyone, I'll take this information to the owner and let him know.

Of course, now that I have all this input, he'll probably just take it to his indie and get it fixed by him...but I had to try, he asked.