A/C overcharged? high engine load, increased running temps, stalled...thx for input - PeachParts Mercedes-Benz Forum

sshanky · #1 04-01-2011, 09:46 PM

Hi, I just had my A/C renewed (80 300SD) and it works well, but it seems to place a LOT of resistance on the engine -- the engine temp gets quite high, about 200F.

But more important, today, I turned off the compressor, then turned it back on, and the engine stalled. Couldn't start it again when compressor turned on. If started again without compressor, then I turned it on, the engine would stall, strange sound from compressor.

I stopped messing around, waited an hour, then it started up fine again.

Isn't there supposed to be some protection to make sure the compressor doesn't turn on when there's too much high-side pressure (is this the correct terminology? I'm learning this today, but I do remember that for example it's bad to turn your house A/C off and then on quickly)? I wonder if the pressure valve on the evaporator/drier is for this function? or is that to just make sure there is enough refrigerant? I'm being told the guy might have seriously overcharged my system.

Thanks a lot...

tangofox007 · #2 04-01-2011, 09:56 PM

Quote:

Originally Posted by sshanky

Isn't there supposed to be some protection to make sure the compressor doesn't turn on when there's too much high-side pressure (is this the correct terminology?

For the most part, that is a feature of R-134a systems. Your car originally had only a low-pressure cut-out switch.

sshanky · #3 04-01-2011, 10:14 PM

So should I be wary of turning on the compressor on when it's hot and has just been shut off, or off and then on quickly?

leathermang · #4 04-01-2011, 10:21 PM

What kind of refrigerant do you have in your car ?
Can you show us a pic of the dash ? There are three types of AC systems in our cars..
Can you show us a pic under the hood ?
We will try to sort this out... but you really do not mean that you are turning on the compressor.... but that you are turning on switches or thermostats on your dash ,right ?
Unless you are saying you have the compressor hard wired to a switch inside the car ?

Tell us everything about the reason you had the system charged or recharged lately... all the gory details... as specific as you can.

sshanky · #5 04-01-2011, 10:35 PM

Hi,
Thanks for replying. I will post a photo later but it is a 1980 300sd (w116) with the old style climate pushbuttons. There is a separate a/c switch to the right of the pushbuttons which directly controls the compressor. As long as the pushbuttons are set to auto lo or auto hi the switch will control the compressor directly.

The Mercedes shop here did the repair and they are a reputable Benz shoo with a lot of experience. They put in a new compressor and expansion valve and receiver/drier, and said they had to flush the condenser due to seeing metal particles on the old seized compressor.

They told me I needed a new auxiliary fan and temp switch, but I repaired the fan easily, tested the switch and circuit according to the service manual
And it works now. It comes on while the car is idling and it is hot out, but only after idling about 2 minutes when outside temp is 95or so.

79Mercy · #6 04-01-2011, 10:39 PM

You need to return the car to the shop. The compressor should not load down the engine that much at all. You be able to start the engine with the compressor engaged. Sounds like the compressor might be starting to seize and its not spinning as freely as it should, or it could be incorrect system pressures...

leathermang · #7 04-01-2011, 10:40 PM

"And it works now. It comes on while the car is idling and it is hot out, but only after idling about 2 minutes when outside temp is 95or so."
I am not sure what you said... can you rephrase that ?
It does blow cold ?
only comes on if the outside temp is 95 or so ? but not at lower outside temperatures ?
Is there ANY squealing of the belts ?
79Mercy is correct about it not properly loading the engine that much... I was trying to sort out if that was really a causal relationship...

So there are NO overheating tendencies of the engine UNLESS the AC is ON ?

sshanky · #8 04-02-2011, 05:21 AM

OK, I'm back on my computer and off of the little tiny phone keyboard! I'll try to be clearer (although I enjoyed all the responses that I could read on my phone during dinner, thanks a lot everyone).

A bit of back story: I bought this car in pretty unknown and a bit rough shape, and have been fixing it slowly over the last six months. I have it pretty well all finished -- it runs great, doesn't leak (much), the servo is fixed (I did it myself, feel free to ask me questions as I have a good understanding of its workings now), the lights and electronics and vacuum all work well, but the AC compressor was the last thing to do. I didn't know what was wrong so I brought it to the MB shop, and he informed me I'd need a compressor, expansion valve, and dryer. He replaced them, flushed the condenser, and charged me way too damn much. Since he knows I know how to fix many things on my own, he didn't replace the aux. fan or temp. switch for the aux. fan, and I fixed those on my own, tested by shorting temp switch, and tested the temp switch too, in hot water, as the service manual instructs. So, now the fan works.

The A/C blows pretty cold, and does rob the engine of some power. I've been driving it with A/C only for a week or so now, so I'm learning its characteristics. But today, it was 95 or 96 here in Phoenix, and the A/C was almost not cold enough to deal with the heat (what will I do when it's 110 here?). When I parked at lunch, I wanted to check to see if my aux fan was running, so I got out with the car running, and checked. It came on shortly after parking. I for some reason wanted to turn off the compressor, so I switched it off in the car. Then, I switched it back on, and the thing made a squeaky noise and the engine stalled. I had no idea why, so I tried starting it, and it would not stay running if the compressor switch was on. Off, it worked fine, but when I'd turn it on at idle, the engine would stall. I went inside and ate lunch. Afterward, it did start but the idle got very low.

Later in the evening, when it was cooler out, the compressor seemed to provide much less load on the engine than it had while the temp was hot, and especially a lot less load than when I turned it off and back on quickly.

Finally, to answer leathermang's question, the compressor goes on whenever I switch it on with the dash switch (photo on this page) and off when I switch it off, regardless of outside temp. Also, I have noticed that even when the AC was not yet installed, the temp. on this engine showed ever so slightly above 175 (normal), but not very much. But this afternoon, the temperature was around 200F, at the 3/4 mark in the temp. gauge.

Sorry about the long novel here, I just want to be clear. Thanks everyone!

vstech · #9 04-02-2011, 05:48 AM

OK.
the aux fan sounds like it's working right.
the a/c sounds like it's got the wrong oil charge... does the bill explain how much oil they put in? the shop flushed the condenser... did they flush the evap? did they replace the TXV? did they replace the compressor manifold? what refrigerant did they install? 12 or 134? what oil did they use? pag or ester or mineral? finally how much refrigerant did they use? the bill should state how many ounces were installed.

tangofox007 · #10 04-02-2011, 07:09 AM

Quote:

Originally Posted by sshanky

But today, it was 95 or 96 here in Phoenix, and the A/C was almost not cold enough to deal with the heat (what will I do when it's 110 here?).

Sounds like you answered the refrigerant question. R-134a, no doubt!!!

engatwork · #11 04-02-2011, 09:13 AM

Quote:

said they had to flush the condenser due to seeing metal particles on the old seized compressor.

There is NO WAY they can flush all the metal particles out of the condenser. They should have replaced it. My thought is that there are metal particles in the compressor and it is on the way to locking up.

vstech · #12 04-02-2011, 09:34 AM

Quote:

Originally Posted by engatwork

There is NO WAY they can flush all the metal particles out of the condenser. They should have replaced it. My thought is that there are metal particles in the compressor and it is on the way to locking up.

this would be true with a parallel condenser, but it's a simple matter to properly flush an O.E. condenser completely. weather or not they did a good job is not known, but it can easily be done.

if it were me living in AZ, I'd source a modern parallel flow condenser from a 90+ 126 or get a higher concentration small tube condenser from an 84+ 126 and then have the system flushed COMPLETELY both coils, and replace the dryer and the TXV and measure in the exact amount of mineral oil per the specs of the car, then recharge with R12.
either that or only drive the car on cloudy days...

hmm I don't know if a 126 condenser will fit in a 116, you better measure one first. perhaps someone here on the forum has knowledge of this swap.
if it can't be swapped, you should pull your condenser out of the car, clean it externally. and make sure ALL fins are straight. when I say clean, I mean SOAK it in commercial condenser coil cleaner. and rinse it completely, then do it again. THEN coat the coil in coil protectant. then get the R12 in there.

Yak · #13 04-02-2011, 10:42 AM

You might have answered your own question(s) early on.

There is a ratio of 134a to R12 if you're converting or refilling, something like 0.8 to 1. The sight glass technique for "fully charged" doesn't work well with 134a. When they charged the system did they specify how much they put in? That might help.

There are different temp switches for the fan for gas/diesel. You want the cooler one that trips at 55 degrees C.

The receiver dryer can be sourced MUCH cheaper than list price, so that should be swapped if it wasn't.

Assuming this was converted to 134, a proper conversion would have retrofitted the Lo only pressure switch to a Hi + Lo pressure switch. You need to evacuate and recharge the system to swap the pressure switch.

To trouble shoot the system they'll need to hook up gauges. Many 134 conversions did not swap the hi side port since "you don't NEED to" in order to fill the system so it's possible that the shop did not really measure the hi side.

The compressor should not act like an engine brake unless it's seizing or overpressurizing. Either one could be occurring based on the rest of the system having been incompletely/improperly flushed or having been oil-starved with bad bearings.

Also make sure the gap between the condenser and the radiator is clear and not filled with butterfly carcasses or mouse nests.

engatwork · #14 04-02-2011, 11:02 AM

Quote:

this would be true with a parallel condenser

oops - that's right. The p flow condenser is the one I was thinking about.
They would have had to THOROUGHLY flush everything and replaced the exp valve too. Even with all this if they did not get all the particles out then you can kiss the compressor goodby.

leathermang · #15 04-02-2011, 11:12 AM

OH, MAN !!! Great answers all !!! It has been so long since we had a thread with no flakes adding untrue junk to it or trying to sell junk refrigerants, etc... what a pleasant start to the AC season !! Thanks Everyone ( so far, LOL )....