evaluating an AC compressor when system is currently discharged - Page 11 - PeachParts Mercedes-Benz Forum

kuene · #1 07-17-2018, 08:36 AM

Cool. Looking at the forums threads. Should I pick up some condenser cleaner foam like that have at Home Depot? And then blow it out with water and air? I’m assuming this liquid wouodnthen make its way out down the trans tunnel drain tube.

Diseasel300 · #2 07-17-2018, 12:38 PM

The foaming stuff works well if you can get it on the coil. I used the concentrated Nu-Brite for evaporators (green bottle) in a pump up sprayer on my SDL because I couldn't get the can of foam in there, the 123 may be more accessible. Consider using a toothbrush on a stick to clean all the muck off of there. Rinse well. Don't be surprised if it's a horror show in there, 30+ years of leaves, dirt, mold, mildew and other nasties don't make for pleasant viewing. Anything you wash off should come out of the evaporator drains under the car. Don't go crazy with the water or you may be cleaning up more than you were bargaining for.

Your reward for a disgusting job? Stronger airflow and improved cooling, not to mention allergies that aren't freaking out from breathing 30+ year old mold!

vwnate1 · #3 07-17-2018, 09:31 PM

I cheated and bought a remote viewer at Harbor Freight, it is incredibly cheaply made but works just fine, it's designed to crap out or loose a part & stop working the *instant* you're not uber delicate with it but for looking in there it's fantastic .

I waited for a cool day and sprayed some foamy cleaner in there and let it soak a bit, flushed with the garden hose (use a nozzle or suffer the consequence !) and never a dribble on the carpets ~ every bit of crud went right out the drain tube everyone touches then complains when it crumbles .

As the evaporator is light alloy you want to try to find proper AC evaporator cleaning stuff so you don't cause corrosion .

kuene · #4 09-03-2018, 09:05 AM

I replaced the evap temp sensor and the compressor is now kicking on and off as is should be. I want to test my original unit, but I’m pretty sure it was the faulty component now.

Diseasel300 · #5 09-03-2018, 09:55 AM

If it's working properly now, I'd find the nearest trash can and insert the old one in it.

97 SL320 · #6 09-03-2018, 05:38 PM

Quote:

Originally Posted by Diseasel300

If it's working properly now, I'd find the nearest trash can and insert the old one in it.

Doing a failure analysis of failed parts gives one a better understanding of how things work. This is vital in building a knowledge base in order to fix something in the future that might not even be AC related. A true mechanic can fix _ anything _ down to the smallest part.

It also gives experience in taking things apart that are not normally serviced. If one is stranded on a desert island or the part is no longer made, these skills come in handy. Not to mention a better appreciation of " how do they make this at such a reasonable cost? ".

Testing would consist of a continuity meter across the terminals, dunking the sensing bulb in a water bath at low temperature and a thermometer checking water temp. I'd probably use a bit of antifreeze to keep the water liquid.

Your switch might have a temperature rating on the side so look at the numbers. It might not, for example, say 5 *C but 05 might be in the makers part number ( not MB part number ) .

The most likely failure point is welded contacts causing the compressor to run all the time allowing the evaporator to ice up. No air flow = no cold air.

If the sensing bulb had lost it's charge, the contacts would not close because the switch thinks the temp is too low and the compressor would not run at all.

Diseasel300 · #7 09-03-2018, 08:09 PM

Failure analysis is great on something that's worth repairing and assuming that the person doing the post-mortem has the ability to understand what it is they're looking at and WHY the piece failed. There's very little to these switches....a sensing bulb, a capillary tube, and a switch contact. You're not going to repair any of the above, so why bother? The new part fixed the problem, the old one isn't going to be repaired, so who cares?

Before jumping down my throat of being wasteful, I'm the type that actually DOES post-mortems on just about everything and have my entire life. Mechanical switches go straight to the trash when they die. When they fail, they're done.

97 SL320 · #8 09-03-2018, 09:30 PM

Quote:

Originally Posted by Diseasel300

Failure analysis is great on something that's worth repairing and assuming that the person doing the post-mortem has the ability to understand what it is they're looking at and WHY the piece failed. There's very little to these switches....a sensing bulb, a capillary tube, and a switch contact. You're not going to repair any of the above, so why bother? The new part fixed the problem, the old one isn't going to be repaired, so who cares?

Before jumping down my throat of being wasteful, I'm the type that actually DOES post-mortems on just about everything and have my entire life. Mechanical switches go straight to the trash when they die. When they fail, they're done.

My first two paragraphs in the prior post address this. I'm not saying to investigate every failed part, do it with a few as a learning experience.

At some point he will run across a part that can't be had at any price making repair the only option. He can develop these skills on an irreplaceable part or something that is zero loss if he fails.

Our guy can learn why the contacts welded. RE: How inductive kick is generated from a non snubbed coil and how it cause arcing / welding of the contacts. See also Mr. Miyagi for my overall reasoning.

Quote:

Doing a failure analysis of failed parts gives one a better understanding of how things work. This is vital in building a knowledge base in order to fix something in the future that might not even be AC related. A true mechanic can fix _ anything _ down to the smallest part.

vwnate1 · #9 09-03-2018, 10:02 PM

"See also Mr. Miyagi for my overall reasoning."

I too am always trying to sharpen my skillset by taking things apart to see what makes them tick ,

Not everyone is so be nice .

kuene · #10 09-05-2018, 10:13 AM

as a rule I've saved every part (unless a wear part like bushing or rotor) that I've replaced on my merc. Partially in case somebody wants it later, partially as a forensic file, partially out of curiosity. Also, sometimes the new parts crap out and I go back to the old part and see if I can fix. (prob not in the case of a commodity part like a temp sensor though)

Next problem I have to face is whether or not my incorrectly clocked (upside down) R4 is going to explode due to lack of proper lubrication. Sure don't like the sounds of the grumbling - thinking of replacing compressor with correct when I switch from the r134 to my r12 supply (now that I know the system is clean and tight). System cools great though.

97 SL320 · #11 09-05-2018, 12:40 PM

Quote:

Originally Posted by kuene

as a rule I've saved every part (unless a wear part like bushing or rotor) that I've replaced on my merc. Partially in case somebody wants it later, partially as a forensic file, partially out of curiosity. Also, sometimes the new parts crap out and I go back to the old part and see if I can fix. (prob not in the case of a commodity part like a temp sensor though)

Next problem I have to face is whether or not my incorrectly clocked (upside down) R4 is going to explode due to lack of proper lubrication. Sure don't like the sounds of the grumbling - thinking of replacing compressor with correct when I switch from the r134 to my r12 supply (now that I know the system is clean and tight). System cools great though.

Leave it go, the R4 has 4 pistons so it will be noisier than a modern compressor with 6 or 10 . Some R4 systems had a muffler on the discharge line to smooth out pulses.

The only clocking is position of clutch coil plug and front bearing oil hole. Dig around a bit and find a find a GM service manual that has compressor repair info, that will be the most accurate source of front bearing clocking info.

Given the system cools fine, just keep the R134, no sense using up the 12.

kuene · #12 09-05-2018, 05:56 PM

i just don't like the grumble/grinding noise it's making though - making me nervous. I listened with my cheap auto stethoscope and it sounds like a grind.

If the r4, even with wrong clocking, is presumed OK for the sake of argument I ask myself: Could I need more oil? It's hard to know total oil I have in system, as I had a bit of a spill during compressor hookup and had to guess the makeup when I shot some in at the top of the suction line.

I was wondering if I should try to add another ounce and then listen, but I'm not sure if there is a way to ad oil without discharging. does ester oil even come in those little recharge compressed cans? or only in normal liquid form?

Diseasel300 · #13 09-05-2018, 06:09 PM

Given that it's working, I'd be inclined to let it go until it craps itself, clean out the condenser, and install another (or do a Sanden upgrade) when the time comes. Reciprocating compressors moan and growl. It's just part of life. The one on my SDL moans at exactly 1500 RPM on the tach (which happens to be driving 30mph). 50RPM on either side and it's silent. My '96 Exploder had a very loud "rattle" from the compressor when it ran. Went over 40K miles from the time it started making the noise until I got rid of the car, never a problem other than the noise under the hood.