1998 ML320 - AC Electrical Issue?

We bought our 1998 ML320 about 4+ years ago. Had it's issues, but what used vehicle doesn't. Currently we have these set of issues:
1. Heated seats stopped working a long time ago (oh well)
2. Rear wiper just clicks (according to one group member here it's a common problem) 3. Starting issue (drive the Benz more then 30 min, stop, walk into Starbucks, come out 5 minutes later and you aren't going anywhere *sometimes* - pain, but a problem that has a solution... wait for it to cool down). 4. AC IS OUT
Prior to it going out completely, when it wouldn't turn on, I would pop the fuse box under the hood, *massage* some of the relays, and BAM, fan would click on. Not so much now. I stopped by one of the auto parts stores and got 2 new relays (the ones I would slightly tap/move back and forth) thinking I might just have a bad relay. No such luck.
Anyone have similar issues? I'm not against taking her in, I'm just looking for a potential DIY fix that might be a quick one and something I can take care of fast - it's hot here, of course. Any suggestions are greatly appreciated. At least the windows work to keep as cool as possible.
Thanks.
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If you are handy with electrical works, you can diagnose this by checking the power at the seat when you trigger the heated seat... if no new power other than your power seat... it is probably the relay.
If you got power, then you need to check the resistance of heater pads... two sets... should read some resistance.
Most likely is the relay.

Change out the wiper motor.

Most likely a leaky fuel injector. You got a vapor lock because the fuel pressure didn't stay high and hot engine coupled with low fuel pressure will make fuel turn into gaseous state... let the dealer fix this.

Get a bottle of refrigerant at the local auto parts... the one with a hose and fittings already on it... hook it up to your syste,... it would be the one with blue cap... The pressure must be at least 60 for the compressor to come on... Once the compressor is running, you will see the pressure drop... it has to be around 25 to 30 PSI range for AC to be COLD.
So that is at least 2 of the 4 you can do.

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Thanks Tiger. I'll jump on the ones you suggested and let the board know how it goes. Appreciate the help.
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Went and got the refrigerant. Attached to the system - 100 PSI. According to the instructions, if it's in that range there's a bigger problem. Have yet to tackle the seats (since it warm enough out here as it is), but thinking it's time to take her in and have the set of items looked at. Thanks for all the help and suggestions Tiger.
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100 PSI means your compressor is not kicking on. That is normal pressure when system is not operating... Are you sure you turned on the AC? Did you check the fuse for AC?
Look by the drier,,, round black thing by the radiator where your AC hoses goes to... the terminals that stick upward... black ... is the wire attached?
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I checked, and all wires are attached. One thing I forgot to mention was the horn stopped working. So yesterday while at the gas station (AC still not working), I popped the hood and checked the fuse for the horn. When I went to remove the fuse, just by touching the the fuse and relay both the horn started to work and the AC kicked on. Not sure what this means?
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LOL... that means the fuse had bad contact... I'd pull it out and reinsert a couple of times... to break out those oxidations... Possible that your fusebox cover was not sealing tight enough.
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Well, never fails. According to the wife the horn now still works, but the AC has gone out again. You mentioned breaking out the oxidations... my fuse box cover isn't the best sealed... could I be getting oxidation that is preventing a strong connection?
She wants to get a window unit and plug that though the passenger window while I continue to explore possible solutions. Thanks for the help - I owe you a beer (or 2).
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I'd double check the fuse again for AC this time... maybe you got a bad fuse too... take it out and check.
If you are handy with multimeter... set it to ohm... and go to that accumulator/drier... the black sensor sticking up... pull the two wires off the top and check the terminals with the multimeter... should read 0.1 or something... continuity is what we are looking for.
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