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#1
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No voltage to AC compressor, what now? (AKA "I'm melting!!!")
When I bought my first MB a few months ago ('83 300SD) my wife dubbed her "The Phoenix", because she is gold with a tan interior, chrome wheels, and lots of chrome trim. She says we look like a retired couple from Phoenix driving around in it, and that my constant tinkering is like trying raise the proverbial bird from the ashes.
Anyhow... when I got it the AC didn't work and there was constant warm air coming out of the vents, but it wasn't a problem in February. Now that it's April but it feels like August and every shirt I wear has to be peeled off the MBtex like saran wrap, I think I better do something about it. The PO said that all it needed was the dryer unit to the left of the radiator, so that was the first thing I replaced. No go. Next up was installing a rebuilt main switch unit in the console and a new monovalve. This took care of the constant warm air issue, but still no AC. Then I tried jumpering 12v to the compressor. This did the trick as a temporary fix, but I can't be telling valets to open the hood and disconnect the red wire running before parking my car. It would embarrass the hell out of the wife, and besides who wants to trust a valet making minimum wage plus tips with such an important task? Yesterday I installed a new relay (the one with a "J" under it in the fuse box) hoping that would do the trick, but no such luck. Where do I go from here? I stand waiting with VOM in hand and sweat beading on my brow... |
#2
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Do you know which AC system you have ? possibilities are ONE, TWO or THREE.
Ok... so when you have the compressor hot wired ( no pun intended ) you have cold air ? Do you have R134a or R12 in the system ...if you know ....? When it is running and cold is your aux fan on in front of the radiator ? Do you have access to a legit vacuum for servicing the system ? You do need to tell us how exactly you replaced the dryer.... everything you did before and after that installation.
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1980 240d , chain elongation, cam marks reference: http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html evap fin cleaning: http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator A/C thread http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html |
#3
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There is a "freeze switch" on the evaporator to prevent icing which can sometimes fail. It happened on my 300sd when the AC suddenly quit cooling. It's easy to test with a volt meter.
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"spreading a trail of obnoxious where ever we go" 1981 300sd w/ 341,500 miles http://www.wecrash.com/pics/ddda_banner.gif |
#4
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Thanks for replying.
Quote:
Quote:
Not sure. Quote:
Quote:
I first disconnected the two lines going in and out. I then unplugged the wires and took the unit out. Installation was a reverse of steps 1 and 2. Did I do something wrong? It seemed pretty straightforward. |
#5
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Will this prevent voltage from reaching the compressor to engage it?
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#6
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Quote:
There is a rigorous procedure for doing this, which includes thoroughly flushing the system (then flushing it again), introducing a measured amount of lubricating oil into the refrigerant circuit that is compatible with the refrigerant you plan to use, pulling a complete vacuum in the refrigerant circuit, and introducing a properly measured amount of refrigerant. Some details omitted.....
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Bob '82 300D Petrol B-G Metallic |
#7
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Quote:
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#8
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More specifically, it will prevent voltage from reaching the compressor relay, as will the low pressure cut-out switch on the receiver/drier. Checking for continuity across both of those switches would be a good idea.
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#9
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Does that mean that you replaced the receiver/drier but you did not recharge the refrigerant?
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#10
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Quote:
If you accurately described your actions, and you did open the system and release the refrigerant, then your pressure will be by definition zero and this would be enough to keep the switch open and the compressor off. When you opened the lines, did it hiss like a mother as if it was releasing gas? If not, your refrigerant was already gone - most likely via a leak. By opening the system and not vacuuming it immediately, you introduce moisture. This reacts with oil to make corrosive acids that eat away at the system internals. The sooner you get it out by flushing the system, the better.
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Bob '82 300D Petrol B-G Metallic |
#11
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Correct. Regarding your other post, under what conditions should I see continuity?
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#12
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Unfortunately, it's possible that you damaged your compressor by jumping the clutch. No refrigerant equals no lubrication. |
#13
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Quote:
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#14
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It's not just possible, it's 100% guaranteed. And if you didn't hear any refrigerant escaping when you cracked open the first fitting, there wasn't any there in the first place.
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#15
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A/C
" It will be off to the mechanic tomorrow for a recharge and testing."
Comprehension has Not Occurred! 1.You have released ALL your refrigerant(and most of your Lubricant) by opening the system. 2.You have CONTAMINATED your system by Closing it up (After R+R-ing the Reciever/Dryer) WITHOUT Properly FLUSHING It. AND then pressure testing with Nitrogen...Then Vacuuming for 24 Hrs. Before installing Refrigerant(+New Lubricant). All a "Recharge and Test" will do is further Destroy your Compressor! Any time a system is "OPENED",It gets a new Receiver/Dryer and Vacuumed. (Smart Money is on always Flushing, Also!) (Compressors are "Hand Rotated" whilst installing New Lube to "Flush" old Lube) [The "Hat Trick" to Success is a pressure test with Nitrogen] The Really,Really Smart Money is on BG's FrigiQuiet Lubricant! (No Acid Formation EVER)
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'84 300SD sold 124.128 Last edited by compress ignite; 04-22-2009 at 06:37 PM. |
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