Yet another Climate Control issue...
 

Just what all you experienced wrenches wanted to read from a Barney like me...

Yet another Climate Control issue...

1983 300 D Turbo (123.133 617)

I recently had a MBZ independent tech troubleshoot the climate control system in my car. He said the push button unit is fine, but recommended a new ACC controller (“electronic switching unit” in the manual), monovalve, and aux. coolant pump in addition to the expected evacuation and recharge. I figured I’d blow off the AC side of things and concentrate on getting some heat--that is until I start sweating my @$$ off this summer, instead of freezing it off.

Thinking I could save a few $$$ I replaced the pump, rebuilt the monovalve, and replaced the ACC controller this afternoon. Only one problem... still no heat.

After exhaustive research and reading of old threads, I already found and tried the following advice from the forums:

“If no heat, you should check the voltage at the monovalve. If at 0 with far left button pushed, your climate control unit is working, at least on defrost”

Checked. 0 Volts found. What are the chances the controller is bad even though it passes this simple test?

“When electrical power to the monovalve is removed, it opens to a ‘full heat’ condition.”

“Disconnect the electrical plug on the monovalve. You should get full heat with the plug disconnected. See if that happens.”

I did, and it didn’t--still no heat--even with the car at operating temperature.

“I have been down the no heat road with a brand new monovalve repair kit. The plunger would intermittently stick in the monovalve body. I found the problem by bench testing it. Remove it from the car and very carefully wire it up so you can apply and remove power from a battery or other 12 volt power source. You should be able to blow air through it with no voltage applied, and it should seal completely when voltage [is] applied.”

It passed the blow test. I am still spitting out the coolant ...

“You can try bypassing the aux pump with copper pipe connecting the 2 hoses and you should get heat while driving if the pump has failed and indeed restricting flow.”

Pump worked fine when 12 volts were applied directly. When installed in the car, I can feel coolant running through the hose after the pump and into the monovalve. I can’t feel any coming out the other side, though. Why not?

“The temp sensor that measures the air temp inside the evap housing or the cabin air temp sensor is bad IF it is not the pushbutton unit. ...disconnect them and see what kind of resistance you get across them. If you don't get any then it is bad.”

Tried this one too. Reaching behind the vents, I could wrestle with the sensor, but couldn’t figure out how to unplug the connector so I could meter it. The manual shows the sensor, but not the connector, so I can’t tell what I’m doing wrong. Any ideas?

“...one way to crudely test the monovalve is to pull the electrical connection. ...touch the electrical connector to the pins - you should be able to feel the monovalve move as you make and break contact. For that matter, you should also be able to feel the pulses of the monovalve at any temperature setting by placing your finger on the top of the valve.”

I can feel the monovalve working--when energized directly by a battery--but can’t feel it working when installed in the car. Is this due to the fact that the interior temperature has not gotten up to a temperature where the sensor would close the valve? Another sign of a bad controller?

Which is/are the likely culprit/s?

Bad ACC controller? It’s a reconditioned one from ********AZ. Any ideas on how to test this bad boy without the plug in tester?

Air bubble in system? Should risk a major coolant spill by taking off the heater hose which comes through the firewall and goes into the engine block to see if there is some type of blockage, obstruction, or air bubble?

Bad heater core? Where is it? How do I get at it? How can I check it?

Possible thermostat problem? Even though the car operates at normal temperature while idling and at highway speed?

Please help, I’m not sure what to try or in what order to try it.

Thanks for reading my rant and offering any sympathetic suggestion,

RSCarey

Maybe the fan brushes on the blower are your problem.

A lot has been written on this site about worn brushes and a lack of heat. It only costs a couple of bucks and is an easy job, supposedly. I will be replacing them on my car sometime soon.

Search for fan brushes 123, or something like that.

Good luck

Brushes
 

Thanks for the idea, but the blower motor seems to be working correctly. It blows, just not hot air.

RSCarey

I'm going to guess it has to do with the inside temp sensor. my 83 is really stubborn about delivering heat. after the engine is warm, i have to cycle the push buttons a couple of times before getting heat. now that being said, are you sure there's no bypassing of the heater core due to a leak? did the heat used to work?

Maybe check this too?

http://www.peachparts.com/shopforum/diesel-discussion/143472-what.html

If it never reads hot, the heat would never come on.

Coolant Sensor
 

Other than swapping a known-good sensor in there is there a way to test this?

More background: I just got this car a few months ago, and it has never produced heat.

Does anyone know any of the ACC controller output voltages for any of the other components than the monovalve? That way I could at least test the brain to see if it's any good.

RSCarey

You can ground the wire, but I dont see any input for that on the temp. control unit. You might want to check your temp dial. Maybe the PO fiddled with it and put it back the wrong way. Also the copper strips could be worn out on the dial or it may need a little bit of cleaning. So it wouldnt give out heat even if the dial is set at max? What about at DEF?

Blower function
 

The blower functions normally, just no heat at any setting.

RSCarey

good job
 

Firstly, let me give you a hearty thumbs up for an excellent job at troubleshooting on the system and to carefully search and follow previous threads.

If the monovalve is working properly, and you have provided every indication that the valve bench checks fine, then it must allow coolant to pass when voltage is removed from the valve.

The only caveat is that the diaphragm cannot be torn. You mentioned that you rebuilt the valve, so, I assume that you replaced the diaphragm or thoroughly inspected the old one for a tear. Any tear in the diaphragm might give no heat, even with the voltage removed from the valve. So, kindly double check this one point.

Therefore, we can eliminate all electrical components as the source of the problem at this point. The valve is open and allowing coolant to pass.

So, the next culprit is the heater core itself. If the heater core is plugged, coolant won't flow through it in sufficient volume to give you decent heat.

Therefore, remove the hoses to and from the heater core. One is usually attached to the back of the head. Connect up a garden hose and carefully turn it on to see what kind of flow you have through the core. This can be a dangerous step, because, if the core is partially plugged, the pressure in the core will get quite high (line pressure.........about 70 psi) and the core is not designed for this. You are looking for massive coolant flow through the core. If you only see a trickle or a very low flow, then you have found the problem.

All other electrical maladies can be ignored for the present time. The monovalve regulates flow through the heater core............nothing else.

Thank you Brian,

I just removed a handfull of goo from the heater core!

I removed the heater hose at the monovalve, and the one going into the block. At first I got no flow through the heater core. So I applied constant but low pressure, let it build up, then released it. Filth, sediment, rust flakes, etc. came back toward the hose end. I did that about four or five times, until a GIANT plug of goo shot out the engine block side.

Now I can feel coolant in the hoses all around!

The air is definitely heated, but not what I'd call hot. Since it's 80 degrees in California, I'm planning to wait for a cold morning to put the thing through its paces.

Thanks for your help,

RSCarey

Maybe it would be a good idea to do a citric acid flush. I believe it involves running on 1 Kilo mixed with warm water in the radiator for a day. http://www.coastalscents.com/cfwebstore/index.cfm?fuseaction=product.display&Product_ID=44

Excellent. I would second the advice of planning for a citric acid treatment. Although you got some foreign material and rust out of the core, it is by no means clear. You'll do better on heat, but it won't be satisfactory on a very cold morning.

When you turn the temperature wheel all the way to HOT so that it clicks into position, the system is forced to heat regardless of temperature sensor input.

I Got Heat! (kind of)
 

After a late-night Home Depot run, I have determined that I do--in fact--have heat coming into the car. Only bad news is that it only comes only out of the passenger side vent, and none of the other vents.

All the vents blow air like they should, so I assume they all work, but I am totally lost as to how heat only comes out of one side and nowhere else in the vehicle. Vacuum issue?

I noticed that the heater core has two lines coming out of it, and based on the goo and sediment that I blasted out of the thing yesterday, I am wondering if part of the heater core is still blocked, while part of it is clear. Would this lead up to the situation I've described?

RSCarey

It's a foregone conclusion that the heater core is partially blocked. You might have disloged one portion of the problem, but, the core is really going to need a treatment. Even with a proper treatment, you might not get it resurrected so that it gives satisfactory heat. Remember that the pressure causing flow through the core is far less than the pressure from your garden hose. The flow rate through a marginal core will not be satisfactory for providing sufficient cabin heat.