1984 190D, recently bought with A/C non functional.
Compressor not kicking in.
Static pressure in A/C reads 90psi.
No voltage at pressure switch.
Removed KLIMA Relay, and bridged the #5 and #7 pins, and Compressor clutch locked and kicked in.
Cold here tonight, so could not feel cooling effect at vents...
Is this as simple and a bad Klima relay?.

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2009 Mercedes ML320 Bluetec

Your charge is low causing the low pressure switch to do its job which is to protect the compressor. Bridge the pins at the switch with KOEO and ensure that the clutch clicks. If it does, then charge the system.

Thanks Larry, So 90psi with the engine off is too low?

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2009 Mercedes ML320 Bluetec

You can't tell anything about the size of the standing charge in the system without knowing the ambient temperature. Read a pressure/temperature chart. A 30lb can of R-22 will read the same pressure at a given tank temp whether it's full or only has 5lbs in it.

Disconnect line to switch and ohm across it (the switch) - it should be closed (0 ohms). If its open (infinity), it's bad. To double check, jumper the connector (bypass the switch) with gauges hooked up and try turning the A/C on. If it runs, and your pressures are normal, you have a bad switch.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

Disconnected preasure Switch reads 0.00 ohms when measuring across the two poles...

When the engine is running with the A/C unit set to A/C max cold I get no voltage at the pressure switch wires, and no compressor cluch kicking in.
I can get it to work if I remove the Klima relay and bridge #5 and #7 tho.

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2009 Mercedes ML320 Bluetec

When I checked the pressures, the ambient temp was about 80degF.
This weekend, assuming I am doing this right, I will jump the Compressor with the gauge set on and get a reading.

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2009 Mercedes ML320 Bluetec

Somehow, I ended up lending my little 190 to my younger son... for 4 months..
Now I have to get the A/C working... cos I am using it now!
So, "flushed" with the success of Ps2cho's A/C thread and the fact he has A/C now I thought I would try...

Ok, so I Vacuumed the system out, and started fresh...
I am not sure what was in it... ... the fittings are 134, but no stickers or reference in my paperwork to say it had a 134 swap..
So, I put in ES12a I had here, as its compatable with both oils and both seals.
I know the system is fully charged now.

I dont get any compressor engagement unless I jump 5 and 7 terms at the Klima Relay, then I get Cold Air at the vents, and pressures are about 50psi low side and 210psi high side at idle at 2000 rpm aprox, I get 30psi low and 250psi high.

As a first step, Can I assume that the system is charged and working, so I can move on to find why I dont get Compressor engagement?

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2009 Mercedes ML320 Bluetec

As always Larry, I am pleased when you give your input and you need never apologise!

As A/C is a black art to me I will need some firm direction here...

In my first post I stated that I have no voltage at the pressure switch... I think I need to post some pics to be sure I am doing it right... also I see some non original connectors in there...
Let me grab my Camera..

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2009 Mercedes ML320 Bluetec

Sorry, got distracted yesterday!

Here is the pic..

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2009 Mercedes ML320 Bluetec

Those connectors all look correct to me. I can understand why you would be suspicious of the long white connectors.

Do you not have Voltage on EITHER side of the low pressure switch? The low pressure switch is one with the green/white wire on one side and the black wire on the other.

Is green the latest color for the high pressure cutout switch?

I though it should be red for some reason- but I'd have to check the car at home to make sure.


Michael

Yes, now that you mention it, the ones I have seen have been red. Maybe it's an aftermarket replacement.

Just to get my silly head right...
The low pressure switch is the one on the left, not the green colored unit?
And what conditions should I be getting 12v at one of the wires?

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2009 Mercedes ML320 Bluetec

Green is correct for his year. It got changed to red as a temp/pressure switch. The green actually changes due to pressure as the red changes due to change in temp (which they figured changed due to heat). I am pretty sure it went red in 92 not positive tho.

Just like in 92 the headlights are different and the stock US wipers are shorter shaft 92 and older compared to 92 and newr (92 having a mid year production).

Grrr...
I got the 190D back from MY son and within 2 weeks it was passed on to my GF's son..
I got it back this week cos the waterpump went.
While I am working on that let me see if I can get the A/C working again!

So, to recap... I should have voltage at the (Green) pressure switch at all times or only when the A/C is on?

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2009 Mercedes ML320 Bluetec