ac not blowing cold, testing mono-valve, temp at expansion valve
 

I have a 84 300d with about 300k on it. The compressor is new and I recharged the system per the direction on dieselgiant.com

I pulled a vacuum to 100 microns before I recharged the system.

The drivers side vent it blowing 70 on an 90 degree day.

When I press the 2 middle buttons on the ACC, they both blow on the windshield. I can not get air to blow out of the 2 center vents no matter what button I press or where the dial is set.

I checked the electrical voltage at the mono-valve when the car was started with the ac on, ac off and heat on and it showed around 12v regardless of what I selected on the ACC.

The clutch on the compressor is engaged when any ACC is pressed except the econo which seems to be correct.

I don't know if the evaporator is fighting the coolant going through the heater core or if I'm low on r12.

Should the mono-valve be open for heat and closed for AC?

Is there a way to test the mono-valve so I can eliminate it from the possible cause?

I don't have an infrared thermometer but I was thinking I could take the temp at the expansion valve and that could help me diagnose the problem. I am going to stick a regular cheapo thermometer on the expansion valve and see what reading I get.

Any other ideas or suggestions?

Thx

pete

As it should. The monovalve is controlled via a switched ground, so there should be system voltage present at the positive terminal whenever the key is on.


On your car, "heat" and "a/c" are not mutually exclusive operating modes. The "heat" is used whenever the temperature needs to be increased, regardless of whether the a/c compressor is on. Selecting the temp selector to the detent "cold" position should prevent the monovalve from opening, however. (Except in the "Defrost" mode.)


Easiest option would be to clamp a heater hose.

I clamped the hose going to the mono-valve and my vents blew only 15 degrees cooler than the outside temp. I may be low on refrigerant and there's probably a slow leak somewhere.

I'm a bit confused on the how the coolant is supposed to flow.
Hot coolant comes out the back of the block by the #4 injector (around the oil filter) and then into a Y connector that enters the center of the firewall.
There is another hose the comes out of the firewall near the brake booster and then it flows to the mono-valve.

The mono-valve then continues to the auxiliary pump. Clamping off the hose going to the mono-valve stopped the flow of the coolant going to the auxiliary pump and the flow of coolant coming out the back of the block.

Is this correct?

If this is correct, I would assume that when the ACC is in the coldest position that no coolant will be circulating from the back of the engine because the closed mono-valve would prevent the coolant from flowing.

This would also mean the ACC tells the auxiliary pump to stop because there is no coolant flowing past the mono-valve.

Am I missing another hose that I can't see?

I would think there should be an even number of hoses going through the firewall, not 3. One line in for each line out.

Wouldn't you want the coolant to flow continuously around the engine and the mono-valve would only control the coolant flowing into the heater core.

Doesn't anyone have any photos or diagrams that show the coolant flow around the engine?

Thanks for all the help.

Pete

That is correct, unless Defrost is selected.


Three is correct.


What purpose would that serve?

Your ACC control box is likely bad. Failure mode default is defrost mode. You should only have it blowing on the windshield with the left button.

The two center vents are just that.....vents, you never get hot or cold air out of them....only in economy mode when the dial is set for the outside ambient temp and everything is operating correctly. then you get outside air directly from them. From personal experience....thats a rare situation.

Personally....if they had asked me...I'd have heat and cold air both available from them.....but they never consulted with me when they designed it.

Apparently, your personal experience is atypical. And they certainly do not accurately reflect the proper operation of the subject vehicle.

In which way?

Let's start with the windshield flaps. Are you aware that the windshield flaps are controlled by a two-stage vacuum actuator? And does that suggest to you that there are three options for windshield flap position?

Not at all what I intended.....just that in a failure mode when the ACC ceases function....by default it will appear to function as a defrost mode. even if its not a true defrost mode. And many people spend time chasing a problem elsewhere that is caused by a failed control module.

And those control boxes do fail at a high rate....crappy design...poor quality. What electronic engineer worth the title designs something where three circuit boards butt up to each other at 90 degree angles and are only connected together mechanically and electrically by a series of solder bridges.

Hopefully, this is not what you intended, either. Because it's quite inaccurate.

So is this. The windshield (defrost) vents should be partailly open in the bi-level mode if the center outlet flap is open. (The center outlet flap should be open if the temp control unit is in a cooling mode.)

The OP didn't comment if he was getting a little or a LOT of air....a failure would result in a LOT of air.

A lot of people have spent a lot of time chasing problems that all end up back at the ACC control module. Which is the single most common point of failure, except maybe arguably the Mono-valve.

I was looking to eliminate those up front as possibilities...

And in my training and experience...you eliminate the obvious and most common problems first (this works in electronics just as well as auto mechanics)....isolating the failure to a section then work towards the specific points to find the ultimate point of failure. You don't go directly to every individual component until you have verified all the control circuitry and the higher level controls. I.E. you don't start trouble shooting a rough running engine by pop and spray pattern testing all the injectors first.

Some people might go about it differently...but I've managed to get to the end result efficiently enough that I've ended up rewriting a number of test procedures over the years. And even shown two veteran Ferrari mechanics how to shave 9 hours off a timing belt replacement on a 308 GTS engine.

But my way isn't the only way to accomplish the job.

I haven't seen any W123 output anything but ambient outside vent air through the two center vents (in the situation I mentioned)....and nothing I have read in the manual that I remember would indicate otherwise. And no...I'm at the office and can't pull out the manual because its at home with my car.

Ok....did some digging around......found something I didn't think I had at the office....and as a result I'll revise part of my previous statement on the center vents.

They should never put out heat or hot air....but should on A/C put out cold air or function as a outside vent.

That would suggest deficiencies on two counts: experience and memory.

The subject vehicle is a 1984 300D, not any W123. (Not all W123's feature the same climate control system.)


In that case, perhaps the best option would be to remove your original (and highly inaccurate) post until you have a chance to study up on the system.

Center vents should supply cold air on the normal setting(center push button). They do not supply heated air at any time.

And pray tell, explain WHY an 1984 300D 123 with the automatic climate control is ANY different than any of the other 1982, 1983 or 1985 that used the same exact control module, and other parts? Except for the manual system. and the older ones with the Chrysler monstrosity.

Someone pee in your wheeties this morning? Then curb the attitude dude. Because nobody was taking one with you.


I've been all over the W123 inside and out over 7 years now and the W116 for 10 years....I'm not a noobie.