W114 A/C

[kavadarci1]

Hi,

Previous owner of my car tells me his mechanic "re-wired" the A/C from the engine bay so it doesn't come on (he didn't want to use it).

Previous owner doesn't know which wire was disconnect/connected/re-wired so I'm stuck with this dilemma now.

When i turn on the fan on with th a/c switch on the lower a/c fan is kicking in but no life from the a/c compressor, the clutch is not engaged thus no cold air.

Honestly i don't know where to start with this problem as i don't know how the wires were suppose to be connected. I am also suspecting that the a/c just might not be working and all the wiring to be correct.

Thank you for your suggestions.

[Pooka]

Check around the edge of the A/C compressor pulley/clutch. There should be a wire, just one, and it will likely be black. If there are two wires they will be different colors.

If one one wire it is the 12 v (+) to the clutch and the clutch is grounded through the body of the compressor. (I am assuming you know that the ac clutch is electric.) If this wire is connected (It should just plug into another wire) then disconnects it and hit it with 12 v. The ac clutch should 'pop' in with a rather distinctive click. If no click then your clutch is bad and needs to be replaced.

If the clutch works then start the car and turn on the ac. Use a voltmeter to see if you have 12 v being delivered to the clutch through the wire. If no 12 v is present (it might be higher, but it should not be lower) then you have found a problem and you will need to start tracking back from there.

This can be put right. It will just take a little troubleshooting.

If you have two wires then one is the 12 v and one is the ground. The ground will likely be brown or maybe white. To test the clutch just ground the ground wire to the engine block and hit the hot wire with 12 v.

To test a two wire power source just hook up your voltmeter to see if you are getting 12 v from the two wire source.

And if your clutch does not work then you just need to replace it.

If all else fails you can take this to a shop that does automotive electrical work and they should be able to troubleshoot it quickly and cheaply.

[kavadarci1]

Thank you
I will check what you suggested and provide feedback.

[Pooka]

When dealing with a problem like this you have to start somewhere and the AC clutch is at the end of the line. It is also easy to get to.

If you have power going to the clutch but the clutch is not pulling in you have found the problem. But if the facts truly are that someone rewired it so it will not come on then the problem could be anywhere.

But check the clutch first. It could be that it was broke and the guy you bought it from was just passing along the story he was told.

[kavadarci1]

Originally Posted by Pooka

When dealing with a problem like this you have to start somewhere and the AC clutch is at the end of the line. It is also easy to get to.

If you have power going to the clutch but the clutch is not pulling in you have found the problem. But if the facts truly are that someone rewired it so it will not come on then the problem could be anywhere.

But check the clutch first. It could be that it was broke and the guy you bought it from was just passing along the story he was told.

So I have three wires (see pic)
Which one is the power so I can bring 12v and test the clutch?
Thank you

[kraakevik]

The black lead is almost certainly the power feed--although I'd check the other blue/white lead as well--the brown lead is the ground




Tim Kraakevik
kraakevik@voyager.net

[JimFreeh]

Originally Posted by kavadarci1

Hi,

Previous owner of my car tells me his mechanic "re-wired" the A/C from the engine bay so it doesn't come on (he didn't want to use it).

I cannot count how many times I read something in an add that says the A/C doesn't work....

Some of my favorites are:

1. Don't know it it works, never tried it. So, you're telling me that you own a car, maybe for some time and you've never, ever tried to run the ventilation without using the A/C? Never used defrost/defog? Oh come on now.... Likely, it's more a case of I tried it, but it didn't seem to work. Let's be honest now. And maybe, if you truly know so little about the car, other claims you make are now pretty suspect.

2. Just needs a charge. No ****, Sherlock. That's because it has a leak. And if it's been a awhile, might as well add in a compressor and a dryer to the cost of replacing what is leaking.

Which brings us to this excuse given to the OP. Why on earth rewire it so it doesn't work? If it works, use it. Maybe the car was overheating? OK, so DON'T use it, but why intentionally disable it? Not using it is as simple as leaving the rotary temp switch on the console alone... Doesn't make sense.

I suspect the system has a broken compressor, or has a leak.

First step for me would be to verify compressor/clutch action. Then verify pressure. You can install a R12 manifold to the taps on top of the compressor, and they have mechanical valves that can be operated by using a robust 1/4" open wrench. These valves can also be used to isolate the compressor from the system, observe the rising stem on the valve, and mid-position the stem.

If you have residual pressure and the compressor/clutch checks out, you be lucky. If no pressure, you've got a leak. Most likely would be the hoses, followed by the condenser (rock hit).

If the sytem has been dead for a while, you can get leakage at the compressor seal when you repressurize.

You can also pull a vacuum on the system and see if it holds (which is good).

If you've got a leak, get a freon sniffer and with the car in a garage (need still air) sniff the system from front to back. You can verify an evaporator leak by sniffing the vents on low speed.

Good luck,

Jim

[t walgamuth]

Originally Posted by JimFreeh

I cannot count how many times I read something in an add that says the A/C doesn't work....

Some of my favorites are:

1. Don't know it it works, never tried it. So, you're telling me that you own a car, maybe for some time and you've never, ever tried to run the ventilation without using the A/C? Never used defrost/defog? Oh come on now.... Likely, it's more a case of I tried it, but it didn't seem to work. Let's be honest now. And maybe, if you truly know so little about the car, other claims you make are now pretty suspect.

2. Just needs a charge. No ****, Sherlock. That's because it has a leak. And if it's been a awhile, might as well add in a compressor and a dryer to the cost of replacing what is leaking.

Which brings us to this excuse given to the OP. Why on earth rewire it so it doesn't work? If it works, use it. Maybe the car was overheating? OK, so DON'T use it, but why intentionally disable it? Not using it is as simple as leaving the rotary temp switch on the console alone... Doesn't make sense.

I suspect the system has a broken compressor, or has a leak.

First step for me would be to verify compressor/clutch action. Then verify pressure. You can install a R12 manifold to the taps on top of the compressor, and they have mechanical valves that can be operated by using a robust 1/4" open wrench. These valves can also be used to isolate the compressor from the system, observe the rising stem on the valve, and mid-position the stem.

If you have residual pressure and the compressor/clutch checks out, you be lucky. If no pressure, you've got a leak. Most likely would be the hoses, followed by the condenser (rock hit).

If the sytem has been dead for a while, you can get leakage at the compressor seal when you repressurize.

You can also pull a vacuum on the system and see if it holds (which is good).

If you've got a leak, get a freon sniffer and with the car in a garage (need still air) sniff the system from front to back. You can verify an evaporator leak by sniffing the vents on low speed.

Good luck,

Jim

x2

[Pooka]

Looking at the wires in the photo, from left to right; call them 1-2-3-4.

Wire one is brown. This is the ground. Use a voltmeter to check the connection between this wire and the engine block. I have never seen one grounded in such a professional way, but then this is an older Mercedes and I have not seen everything.

Wire two appears to be connected to a terminal block.

Wire three appears to be connected to the other side of the terminal block.

It is possible that two and three are just mounted there and go to something else.

Wire four is the 12 v (+) to the A/C clutch. Find a 12 v power source, like the battery of the car, and run a line from the (+) pole of the battery to the black wire. The clutch should engage with a loud snap.

If so, your clutch is good. On to the next step of tracking back the 12 V to see why it is not engaging the clutch.

By the way.... Some of these early cars had a low pressure switch that would shut down the electrical system if all the freon was gone. You can see if you have any pressure on the system by 'borrowing' a set of gauges from an AutoZone, hooking it up, and seeing if you even have any pressure on the system.

If not then you need to re-read what Jim wrote since this just got real complicated.

There are only two subsystems to an early A/C system. Pressure and the electrical system. Both have to work, so determine first which it is and almost 50% of your work is done.

[benzfan109]

I have a '72 250C with the same setup as yours. The ground is the brown wire and is correctly bolted to the compressor. The blue wire with the white stripe is the 'hot' for the clutch and the black wire is the clutch wire. The blue wire with white stripe and the black wire should be connected together under one screw. It does not matter which terminal you use, as the connector block is made for two single connections - in this case one terminal is left blank. If your compressor is not locked up and the clutch is in working order, the compressor should run. If the system is charged, you should get cold air.

The heating/air conditioning system in your car has two seperate blower motors. The two blower motors are 'switched' by vacuum which is controlled by the AC knob on the console. At least that part of the system seems to be working as you said earlier.

Let us know what happens after you correct the wiring.

Tom

[kavadarci1]

So
I did the wiring and the clutch is kicking in
I can hear the pump working but there is no cold air in the cabin
Hoses are hot and I can release little bit of pressure.
What's next?
Thank you

[JimFreeh]

Originally Posted by kavadarci1

So
I did the wiring and the clutch is kicking in
I can hear the pump working but there is no cold air in the cabin
Hoses are hot and I can release little bit of pressure.
What's next?
Thank you

Evacuate and see if the system holds vacuum.

Jim

[kavadarci1]

How do I check if the system holds vacuum?
What type of freon can I use to recharge, maybe add oil too.
It says R12a on it, can one still buy this and if not is there equivalent

By the way what is the proper procedure to turn on the a/c and should cold come from the lower part of the center console or from the sides?
Thank you

[Pooka]

To check for vacuum you will need a set of gauges and a vac pump.

If you live in a big city you should be able to rent both.

Instructions on how to pull the vacuum can be found on the net or youtube. I pull down to 30 inches, which the pump will pull down to in a hurry, and then let it pull for about 15 minutes. Then close the valves on the gauges, shut off the pump, and see if the vac gauge holds. If it holds for 30 minutes then you are OK and just low on R-12.

Correct the wiring first.

You can still buy R-12 through a shop but they will have to install it. You will be stunned at the price. You can buy R-134 right off the shelf and install it yourself, but this would require converting your system. This is not a big deal, but it is too complicated to go into here. Again, you might check for a video on youtube.

Right now it sounds like the wires were moved to keep the compressor clutch from pulling in and the system just sat there for who knows how long. With no movement of the oil in the compressor the seal on the main shaft of the compressor dried out and shrunk and most of the R-12 bled out.

It might be time to just take it to an A/C shop. Check the rental costs of the equipment you need and then call some shops to see if they are that much more expensive than renting the equipment and doing it yourself.

And don't forget: If there is an Autozone near you they may have the equipment you need for 'rent'. If so they will let you use for free.

[kavadarci1]

Here is a listing at Canadian tire store for r12
Not expensive and available
Should I just try adding this and some oil and see how it goes

RED TEK Aerosol 12a Refrigerant Can, 6 oz. | Canadian Tire