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AC Troubleshooting
I've had about enough of the sweaty car rides so I'm going to tackle the AC system next week. I don't know where to start however because the system never worked in the first place, and I'm not positive the rest of the climate control works correctly. I replaced the CCU and blower motor with used ones. I don't believe I have any temperature control though. How can I tell what needs to be fixed/replaced? I'm guessing I have to replace the compressor, drier, and expansion valve. Is there anything I should test before replacing these parts?
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1983 300D TurboDiesel |
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Well, for starters, check all the fuses and the relays as well.
What on the system does work? Does the heater? How about when moving the wheel from heat to cold, does the monovalve close? While you are replacing the compressor, drier and expansion valve, have the system pressure tested for leaks, say from all the hoses, condensor and evaporater core. Check the wiring to the compressor, aux fan, and also replace the temp switch on the drier and the pressure switch. Others will chime in. This is just off the top of my head. Also search the forum. Lots of good HVAC info.
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RRGrassi 70's Southern Pacific #5608 Fairmont A-4 MOW car 13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete. 91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K 90 Dodge D250 5.9 Cummins/5 speed. 400K |
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May get lucky and find out that you just need some freon...compressor won't switch on if the pressure is too low (unless you jumper the pressure switch)
Thorough diagnostics can save you GOBS of time and $$$.....ask me how I know. Looks like I bought all the parts you just mentioned only to find out that my problem is either a $40 evaporator switch or a $30 relay (or both). You will definitely find lots of help here, but you have to be prepared to do lots of diagnostics to guide your guides. First thing one of the gurus (Larry Bible is my guess) will ask is what the high and low side refrigerant pressures are....of course to supply this info you will need a manifold capable of measuring the pressures. Good luck - there are few things I have done on my car that have been as satisfying as fixing the AC!
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Current Mercedes 1979 maple yellow 240D 4-speed Gone and fondly remembered: 1980 orient red 240D 4-speed Gone and NOT fondly remembered: 1982 Chna Blue 300TD Other car in the stable: 2013 VW Jetta Sportwagen TDI / 6-speed MT |
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Be prepared to replace all the orings.
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http://superturbodiesel.com/images/sig.04.10.jpg 1995 E420 Schwarz 1995 E300 Weiss #1987 300D Sturmmachine #1991 300D Nearly Perfect #1994 E320 Cabriolet #1995 E320 Touring #1985 300D Sedan OBK #42 |
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I too have to go through this. The A/C failed on my W123, it is inop in the W124, and was working when I purchased the W126.
I am hoping to get our 2 wagons 'chilling' again.
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83 300TD (need rear wiper assembly dead or alive) 84 300SD Daily driver 85 300TD almost 400k miles and driven daily. 98 E300D *sold 86 300SDL *sold and made flawless 10 hour journey to new home. |
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ME TOO! I just posted pretty much the same question before I scrolled down and saw yours. I'd like to know if there's a step-by-step guide, book or DIY thread that I can print off and take out there with me. I've always wanted to learn how to not pay somebody else to do this. Now that it's getting near 100* here in Missouri, I want to know even more! Thanks for any replies to saludayakers question. (I just ordered and received the control switch for the dash panel and was contemplating ordering a new compressor. But there's got to be a good tutorial somewhere on the subject.) I'd say this is the place to find out.
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"Knowing is not enough, we must apply. Willing is not enough, we must do." Goethe *********************************** 1951 Chevy 3100 2003 Indian Chief Roadmaster 1983 GMC 1 ton Dually 1982 Chevy 1 ton Dually, service body (sold) '90 GMC Suburban 6.2 "SS Veg-Burban" (single tank WVO\diesel conversion) SOLD '81 300D ~ Mama's car...my job (now my car)(but still my job) SOLD '83 300sd ~ rescue car SOLD 2005 Ford Taurus (Mama's new car)(NOT my job!) |
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A/C is not as difficult as you may think
ac still not working after ac conversion 87 300SDL
Post #70. Excellent write-up. Search the Internet and there is a wealth of info on the fundamentals of A/C. There is nothing to it as far as the theory goes. The issue is the MBZ Control unit is difficult to understand, but it is like any high tech stuffs. Once you introduce computer or electronics into the system, the complexity goes up exponentially.
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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed. W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html 1 X 2006 CDI 1 x 87 300SDL 1 x 87 300D 1 x 87 300TDT wagon 1 x 83 300D 1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry. |
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Here's the mother of links on Climate Control: Climate Control:
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92 300D 2.5L OM602 OBK #59 |
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Quote:
Told ya Listen to the man - get some gages....not too expensive, cheapo ones from HF or AZ will do the trick for your needs.
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Current Mercedes 1979 maple yellow 240D 4-speed Gone and fondly remembered: 1980 orient red 240D 4-speed Gone and NOT fondly remembered: 1982 Chna Blue 300TD Other car in the stable: 2013 VW Jetta Sportwagen TDI / 6-speed MT |
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Thanks for all the good beta. To be honest I'm not sure if my compressor is kicking on or not. I never heard it so I just assumed it wasn't engaging but from what I've read they can be very quiet. Also it's interesting to note that the compressor will not engage if it's too low on refridgerant. When I have some gauges I will check the levels of the refridgerant and go from there.
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1983 300D TurboDiesel |
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I should also note that I don't believe my monovalve works properly b/c I wouldn't really get cold air this winter. It's a little hard to tell now but it seemed like the only warm air I got was the air that was sitting in the vents for a while and after the initial 5 second blast of air after turning the blower on the air would go back to just a little warm.
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1983 300D TurboDiesel |
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Ok, so here's a basic question that I hope I don't get flamed for: How is the AC supposed to work? Which buttons control what? If I have the temp dial on cold will the AC automatically come on?
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1983 300D TurboDiesel |
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Get the Service Manual on CD. There's a section on the Climate Control. The schematics are pretty crummy quality, but the section on testing all the parts has better diagrams, and walks you through all the tests. The special tool isn't necessary if you read the schematics - all it really does is switch the test points so you don't have to move your meter. Most of the test points are through a connector on one of the control units. You can check all the sensors and inputs to the system this way and you will begin to get a good understanding of your system. Once you rule out the electrical items, then you can go into the engine compartment and start ruling out the mechanical portions.
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mjk '84 300SD 119KMi (Liesl der Diesel) '84 300D 326KMi when the oil left (former parts car) '82 300SD 253KMi (new parts car) |
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