It might be a Torx ( star )

So I couldn't get the bolts out so I took the entire evaporator out, which was surprisingly quite easy. It's just sitting inside the compartment behind the blower motor, no bolts, no screws. All that is required is to remove the wiper arm, the blower motor, and the plastic covering. You can also access the vacuum actuator for the floor vents too. I decided since I had the evaporator out, I would clean up the area, so I took everything out and scraped off old foam, cleaned up leaves, and hosed everything down. When I reassemble it I want to insulate the area. I also got rid of those expansion valve bolts and replaced them with 2 new bolts. I covered the openings of all the ac components to reduce the risk of contamination. I will order the parts tomorrow

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1990 190E 3.0L

Ok, guys. I replaced the expansion valve, receiver drier, o-rings, and vacuumed the system, guess what.....My compressor will not turn on or engage. I can turn the clutch by hand, there is some resistance, like the visco-fan, but I can't get it to turn on and I've add the refrigerant

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1990 190E 3.0L

Did you try shorting the low pressure connector at the drier/receiver?

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Or perhaps it isn't plugged in.

Definitely was plugged in. I tried shorting the two connectors at the receiver drier and nothing. So all in all I spent about $300 maybe, messing around with this and countless hours. I went and bought a new compressor today. Never did the job before, but got the 4 bolts off with ease.....should've known nothing is easy when it comes to these cars. 6mm hex in the middle is a total pia to get out. I had to drain the ps fluid, d/c the brake booster hose and move several other things around to get to it.....And guess what? I stripped it. So I'm done. I'm taking it to my mechanic in a week or so to have him get the bolt out and install the compressor and charge it for me. Lesson learned.

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1990 190E 3.0L

Why are you randomly throwing parts at the car? ( compressor ) Did you check for power at the compressor before saying it is bad?

Interesting that you pointed that out. I did check the connector going to the top of the compressor, but I only got about .2v then I checked the high pressure connector and got about the same. I switched off the car and it went to 0. Is this right or should it be 12v? I tried jumping the connector and got no engagement. Also, I am not sure, but my fuse panel doesn't seem to have an a/c fuse. There is a relay that controls the fan, which also controls the a/c according to what's listed on the fuse panel cover and there is another relay next to it for high speed fan.

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1990 190E 3.0L

The compressor clutch needs 12V to engage. ( you will see near whatever is charging system voltage with the engine running ) The 0.2 V is just stray voltage. Also, when checking, an incandescent test light is a good tool as it will load the circuit where a digital meter won't and can give the impression that power is there but when you plug in the load it goes away.

Make sure you are checking the clutch connector, sometimes there is a rotational speed sensor on the compressor. The clutch wire will come from the pulley area.

Did you replace the expansion valve and have the system recharged right now? Your post is a bit unclear.

Ok, so am I testing the 3 prong-holed wire connector that comes from the wiring harness to the compressor, or am I testing the 3 prongs that are on the compressor? The expansion valve and drier were replaced. System was charged, but no engagement.

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1990 190E 3.0L

Didn't you just go through all of this in 2010? New compressor, etc.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

The compressor clutch will use 2 wires ( sometimes only one as the ground is picked up on the compressor housing. Do you have a wiring diagram?

Had the new compressor/completel overhaul in 2008, the 2010 issue was probably the leaking heater valve, hence my remedy by removing aux water pump and adding a ball valve in its place.

I don't have a wiring diagram unfortunately.

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1990 190E 3.0L

If this has a MAS relay, did you check that? In other words, did you check the A/C relat? In my son's 1990 300e, since 12v was present when the two leads from the low pressure switch were jumped, something upstream from the clutch had to be the culprit. I replaced the MAS and bam... the clutch came to life.

Apologies if this has been already discussed here, I didn't take the time to read the first 2 pages- sorry.

AL

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

Got the compressor off. Had to use the Irwin stripped/rounded bolt head removal tool to get the hex holding the hoses to the compressor. Put it back on, now vacuuming it down to check for leaks. Old compressor looks pretty rough. Mostly all the wiring was stripped, tons of grime and sand all over it.

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1990 190E 3.0L