W123 air conditioning

[Jacob]

1983 300TDt (converted to R-134a) Why does it take such a long time for the A/C to begin to blow cool? The compressor seems to engage right away, but the fan will wait 10 minutes or more to start blowing low and several more minutes to blow higher even when selected on high. After it begins to cool it works fine until the engine is switched off for a minute (fuel stop), and then it's another 10 minutes or more of high desert heat. This problem seems to have been slowly developing over the past couple of months.

[dmorrison]

How was the conversion done? Correctly or a quick fix. Correctly is a complete flush, new Orings, new expansion valve if needed, new oil and the freon.
Quick fix. Add the R134a can with oil, Add more freon and it will blow cold. BUT your compressor will die in a year or so. Then your doing everything list above and more!

Second. Can you put the fan switch on high and it blows cold and at a high fan speed? If you can't then your AC control unit may be bad.

More info please?

Dave

Jacob,

Dave offers great advice. This is no surprise since he just COMPLETELY rebuilt a 123 system like yours. What he didn't tell you was how thorough HIS conversion was. By adding a parallel flow condensor to what he listed, he probably has a 134 a/c that cools better than the factory R12 systems. After his project and the success of the project, I would consider Dave an authority on the 123 system.

The key is condensor capacity. When changing to 134 you lose about 15% of your cooling capacity. The only way to make it up is with more condensor capacity.

An improperly converted system is a great example of "pay me now or pay me later. I agree with Daves comment about your current problem likely being climate control rather than refrigeration.

Good luck,

[Jacob]

Larry and Dave,
Thanks for the response.
The conversion was done by evacuating the R12 and adding R134 and oil. No other parts were replaced. There doesn't seem to be any major leaks as I have added only one 12oz. can since. The system has adaquate pressure when it finally decides to start working - after 10 minutes of driving or running in the driveway. And it cools as well as can be expected, dropping 100+ outside temps to around 45-50.
The conversion was done last summer and has been through it's paces here in Albuquerque for over a year.
When I begin driving with A/C on and fan switch on high, the fan will begin to blow low after 10 minutes and over the next few minutes will step up to high. I then switch to medium when comfortable. As I recall the cooling used to begin in a matter of seconds, not tens of minutes.
How do I trouble-shoot the climate control?
Dave, can I get the details of your conversion project?

Jacob

This is an immaculate car with 120k miles and a recent conversion to a 4-speed manual transmission. I really like it!!

[engatwork]

It should not take 10 minutes for the fan to start blowing. I am thinking you may have an issue with the temperature controller (I think that is the name of it) that is located behind the glove box. I can provide a p/n later today if you need it.

[Jacob]

OK, here's what is happening. When the car is cold, as in the morning - as opposed to sitting in a hot parking lot all day - the fan will blow high for a couple minutes when max is selected, then slow down to nothing. This occures whether A/C is selected or not. It will blow cold for this short time if A/C is selected. It still will not blow cold for a long while when hot (afternoon).
Does this sound like the temperature control unit?
Thanks,
Jacob

Jacob,

Remove the glove box and look for a hose running horizontally from a plastic pipe in front of the glove box over to the temp sensor in the center of the dash board.

If it is not there, go to Home Depot and get a length of foam pipe insulation. Cut it to length and slip it over the temp sensor connector and the pipe. Don't use plastic or rubber hose, they conduct too much heat. There was originally a foam hose in place.

Good luck,

[Jacob]

Here's a little more info.
The foam hose is in good condition.
When the 'ignition' is switched on, the fan will blow high for a minute or less and then drop to little or nothing. Then comes a honking, reedy sound and a low variable frequency pulsing sound to the fan itself.
I did a 'smoke test' at the small vent in the top center of the dash and saw no apparent air movement. (Matches can sure stink up a car!!) Shouldn't this vent be moving a bit of air at all times? Where is the little fan located? (I know where it is on Patti’s 190e).
The refrigeration is functioning, as a bit of cold comes thru the vents while driving.
After a while the A/C will blow cold with a variable fan output, even when high fan is selected. Automatic fan will do the same.
Does this point to a temperature control unit problem? Where is this located? How do I trouble-shoot it?
Was ist los?
Thanks,
Jacob

[dmorrison]

Lets back up here a little. Remove the passenger underdash panel. That is where the fan is located. Either remove the fan by unscrewing the 3 bolts or just apply leads to the fan. Lets make sure your brushes inthe fan are OK. AFter removing the fan apply 12 volts to the unit. Be careful it will torque out of your hand if not held tightly. Does the fan operate at full speed. Or does it vary. If it does not operate at full speed then your brushes are bad and need to be replaced. Do a search for that.
this test will eliminate the Ac control and resistors etc.
Get back to us with the results.

Go here for the 123 Manual job 83-120

http://skinnerbox.steaky.org/123_DISK2/program/123-cd-index.html

Then we can test the AC control and or vacuum elements. But with the low flow, varying speeds and noise I'm questioning the brushes and bearings of the fan.

Dave

Just a note. The tempreature control for the AC unit is located just next to the expansion valve. It will try to maintain a proper evaporator temp. If the blower is not blowing air over the evaporator then it will tell the compressor to stop supplying freon. The blower motor adds heat to the evaporator by blowing warm air over it. If the blower is not working the compressro provides a little freon, it cools the evaporator and the temp probe that stciks into the evaporator senses a cold evaporator. Not wanting the freon to cause the evaporator to allow the temp to drop below 35-37 degrees, or it will ice up. It tells the compressor to turn off.
This is why I'm suspect of your blower.
Also If the system was not flushed we may be dealing with a compressor problem. Its whats called "black death"
Look here.

http://www.ackits.com/index.cfm?fuseaction=black%20death

But lets look at the blower first.

[Jacob]

Thanks Dave,
The main fan is doing fine, it will funtion at full speed,steady and quietl when applying 12v. However it does change speed while operating normally, indicating to me that something else is telling it what to do.
My question was about a little recirculating cabin air temperature sampling fan that controls the rest of the system in other M-Bs I've owned. Am I saying that correctly? Do the W123s have such a thing? I can't find the critter.
What is the little tiny grill top center of the dash? How does this play into the grand scheme of things? Should this little grill be pulling air past a sensor? There is no air movement here.
OK, I'll go plunder thru my 123 discs and see about learning some more about the A/C system.
More later, Thanks again,
Jacob

Jacob,

Dave can answer for sure, but I don't think the 123 chassis has the sampling fan as do the 201 and 124 chassis.

Dave is EXTREMELY knowledgable about the 123 climate control system. Follow his instructions and he will lead you to the Promised Land of cold air.

Good luck,

[dmorrison]

Your temp sensor is located on the top of the dash just above the 2 center vents. This unit has a tube that is connected to the fan housing. the AC fan is what pulls air through the temp sensor. From the sensor a hard plastic tube is connected to it. This tube goes along the underside of the top of the dash. At the glove box area the hard plastic tube is connected to a foam tube. On the right side of the glove box the tube again becomes hard plastic and goes downward to the far right side of the heater box where the fan is located. So if the foam tube is fine, the mechanical part of the temp sensor is OK.
What controls your fan speed is a combination of the AC control unit and the fan selector switch. The top button is the stage 6 or high speed. It by passes all imputs and runs the fan at the 6th stage. The middle white/clear button allows the fan to operate at stage 2-5. The lower button operates the fan at stage 1, no matter what the temp setting is at. In the middle auto position the AC control panel controls the fan speed and evaporator temp based on the input to the temperature sensor on the dash.
The AC units have been known to have cracked circuit boards which causes a break in the circuit. You may very well have this. Your AC board may very well be messing up. Do a search on AC contol panel.
check this site

http://207.210.95.34/~boostd/

I have not, knock on wood, had to mess with any of my AC control panles.

Dave

PS use the service CD you have adn check the temp sensor. YOu will measure the resistance based on the amient temp. Its in the service CD.

[Jacob]

I've been under the dash and seen the plumbing you're talking about.
By the process of elimination it is beginning to sound like the A/C control unit.
The fan switch does not seem to have control of fan speed. Are you saying that the top button should make the fan blow high speed, no matter what? Sometimes it doesn't blow at all, regardless of what is selected.
I'll check the temp sensor and may have to go so far as the control board.
Thanks for the web site, always looking for more sources of info/understanding about my cars.
Although this is a new sort of problem, whenever I get into something I appreciate the engineering of the W123 more and more all the time.

[engatwork]

Look for the silver, cigarette sized aluminum box mounted underneath the dash behind the glove box. Should say temp controller on it (or something like that). Try replacing it with one that you know works to see if that is the problem. I suspect that is causing your problems.

[Jacob]

I think I got it!!
I was fooled onto thinking that the fan was fine because it would run strong on the bench and then quit running soon after starting operation in the car. After re-soldering the temperature control with no improvement, I decided to replace the brushes in the fan motor. VIOLA!!
See: http://207.210.95.34/~boostd/
The proof test will be tomorrow after a long day in the hot parking lot.
Thank you all, especially Dave, for your patient indulgence.