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  #1  
Old 07-14-2003, 11:23 PM
Greg Martin
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air conditioning questions

My 85 300D sedan, I was told, has a bad compressor, won't even rotate, and my 300TD wagon, which had an r134 conversion, is blowing warm. Also, had been (and still am if still for sale) considering Holson's 300CD which needs a new compressor.

After reading some posts here I decided to look into ac - with several cars to fix it becomes worthwhile.

I think leathermang (not sure) recommended www.ackits, and has a site with a number of very useful repair processes, including ? a condenser replacement. [leathermang: can you give me your site's url? I foolishly didn't bookmark it!]

Went to ackits and ordered a guage set (R134) to start on the wagon, which hopefully just needed additional refrigerant, and the Mastercool AC manual. Later get more tools and move on to the compressor replacement in the sedan... Maybe convert to r134, change to parallel flow condenser.... Whatever.

Ok. ^&(*&^*^*^!!!!

First question - where in blazes is the high side port on a 123 with the R4 compressor? The low side port, at least apres r134 is right on top of the engine behind the radiator. Nice blue cap and snap on fitting. The illustrations from the 123 cd showing the service ports located on the compressor would seem (to me) to illustrate another compressor altogether. I can't find anything that looks like a service port. When I find it I'll probably need some sort of adapter. Can anyone help me locate the port and tell me what adapter I might need? (Since I can't find it, I can't say whether a standart r134 hi side connector was installed - that would be a nice surpise!)

Ok - 2nd question.
I though I might as well check the low side pressure, which turned out to be about 12 gpsi, which did seem low to me. Although I know it's not recommended for r134 systems without evacuating the system, I connected a can of r134 to the charging line, opened the valve, and saw the pressure rise to 50-60 gpsi. However, after 20-25 minutes (with the engine running and ac on) very little refrigerant was sucked into the system. (Can weight stayed about the same as another full can.) AC didn't start cooling. Which suggests I have some additional problems. Which knowing the hi side pressure might help diagnose...

Any thoughts and advice will be welcome. Thanks.

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  #2  
Old 07-15-2003, 12:23 AM
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Ports,

Low side should be on the line in front of the engine somewhere infront of the passenger side. Close to the airfilter ish?

High side, look at the condenser line, it runs to the dryer and the other side runs close to the Alternator along the bottom of the engine to the a/c compressor.

You've got to get enough freon into the system to over come the low pressure cut-out switch. If a system is evacuated, in this 100F weather, a little can shaking is all that is needed.


Michael
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83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E
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  #3  
Old 07-15-2003, 12:55 AM
Greg Martin
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Tomorrow I'll run the car up on ramps and crawl around underneath to see if I can find the hi side fitting. Of course once I identify it it'll be obvious.

The system wasn't evacuated. It was reading 12 gpsi when warmed up with the ac running 10-15 minutes. From the MB 123 cd info, which gives a low side pressure/temperature graph for normal operation, I was looking to get to a pressure of something over 2 bar, about 30 psi, when I hooked the charging cannister up; I saw an immediate rise to 50-60 gpsi, which might mean I have overcharged it? There was little flow from the cannister to the system.

Obviously I was looking for a quick and easy fix, without fully understanding the system. Previous service records indicated an annual or semiannual need for additional refrigerant, and I hoped this would quickly put me back in business, while I was learning more details of ac operation. I'm not sure where I stand, now.
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  #4  
Old 07-15-2003, 10:25 AM
Greg Martin
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Tuesday am -

OK - found the little bugger. Right behind the alternator.

[ locating various parts on my Benzes is a continuing challenge
to this diy'er. ]

Of course this morning it's only 70 degrees, and started to rain on me as soon as I connected up the gauges. AC may not even be kicking on; in any event, low side about 30 psi, hi side very low, about 10. I would think either the compressor is not even on (likely if the ac isn't even kicked on by climate control!) or I have a compressor malfunction. Though the diagnostics section of the Mastercool manual suggests hi side pressures of about 121 psi in this event.:confused
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  #5  
Old 07-15-2003, 12:28 PM
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Greg

Some of this may help.

This inexpensive vacuum pump from ackits.com is a neat way of pulling a vacuumn if you have an air compressor.
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  #6  
Old 07-15-2003, 01:18 PM
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Re: air conditioning questions

Quote:
Originally posted by Greg Martin
I connected a can of r134 to the charging line, opened the valve, and saw the pressure rise to 50-60 gpsi. However, after 20-25 minutes (with the engine running and ac on) very little refrigerant was sucked into the system.
Did you turn the can over so the liquid would run in instead of gas?

M.
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  #7  
Old 07-15-2003, 01:26 PM
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You don't want liquid being sucked into the compressor-

JUST SAY NO!!! Only vapor or you'll bend the reed valves.

THey still use reed valves on R-4's????????
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83 300d
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66 Chevy Corsa
68 GMC V6 w/oD
86 300E
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  #8  
Old 07-15-2003, 01:42 PM
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It bears repeating what samiam4 says. You must first establish a vacuum, connect your freon can, purge the feed line, attach the line to your vacuum gauge set, and commence filling by holding the can vertical with the orifice on top. The vacuum will suck in the first of the gas, which you can help by holding the can in a warm (not hot) water bath like this. This procedure is specifically addressed in the MB factory manual.

After the first of the gas is sucked in you can switch on the engine with a/c on full, temp on minimum and you will hear the compressor clutch click (even over the din of a diesel) as the compressor kicks in and more gas is sucked in.

Remember to charge only through the low side - the high side valve on your vacuum gauge set should be closed once your vacuum is established, and remained closed throughout charging. Disregarding this instruction can be life threatening.
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  #9  
Old 07-15-2003, 05:11 PM
Greg Martin
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ThomasSpin -

It was your post that I read that got me started with ackits, and your air conditioning slide show that had the compressor replacement. Thanks much.

Ok - I now understand that I should put the coolant can in warm water to start the recharge. But should add as a gas (neck up) rather than a liquid (neck down).

I'll check the high side pressure later this afternoon after work - temperature should be sufficient to kick on ac. Then I can see if I have hi pressure. I think the reading was not 10 but about 25 psi this am; about 1/2 the first dial marking of 50 psi on hi side. If the belt's not slipping, and clutch is engaged, I should have hi side pressure; if not, I would think compressor probs or major hi side leak!

I'll update later this afternoon. Thanks for all comments and advice. - Greg M.
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  #10  
Old 07-15-2003, 07:43 PM
Greg Martin
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Ok - this afternoon the temperature's 85, and with ac on full I found the following -

1. with refrigerant can in warm water, gas transferred to low side ok.

2. initial pressures - low side 10, hi side very low (5-10)

3, on charging, low side went up to 50-60, hi side went up to
about the same; gradually fell back to previous levels.

4. applying 12v+ to either lead on the pressure switch at the drier/receiver, I did not hear a click as the clutch engaged. Of course, to complicate matters, I have a high frequency hearing loss. (Worked in a factor for a while when younger.) Still, I think I should be able to hear it.

Looks like I have some work in store for me....

Does it sound to you that the clutch is bad?

I know I can get an R4 clutch separately from the compressor. How can I test the compressor? If it's bad, I'd just as soon replace both as a unit rather than find out I need to later. One possiblity might be a just a bad clutch coil - if shorted or open I should see it with an ohmmeter.

The PO had this system converted to r134 in Feb 2002, by Glen's Auto in Shrewsbur PA. They replaced the compressor with a rebuilt unit, changed the "accumulator", added the conversion service port fittings, 6 oz of "refrigerant oil." (mineral, ester, or PAG??) Is anyone familiar with their work? Three months later they added additional r134.

What is recommended r134 conversion for this system? Are original hoses ok?

Any thoughts on what I should do next will be apprecated.
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  #11  
Old 07-15-2003, 11:00 PM
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Sounds like you've got work.

R4 compressor rebuilds are not reliable ussually. They are cheap(aka $79). You can order a new one through Autozone.
If the hoses are not leaking, you can reuse them. All oil needs to be removed. The oil used in 134a systems attracts moisture, very badly.
Then naturally, accumulator and expansion valve. Shrader valves and all o-rings. Replace any obviously leaking or old hoses. High pressure hoses are cheap. Low pressure and manifold hoses can be rebuilt. You'll probably want to relay the a/c fan to run when the compressor is on. Also, the fans do fail-make sure yours spins easily. You'll spend $350-600.


Michael
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86 300E
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  #12  
Old 07-15-2003, 11:36 PM
Greg Martin
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My question re the original hoses was really whether they were good for the r134 conversion. I'm not sure it was really done correctly. The Mastercool manual suggests that because of the smaller molecular size of r134 (less than r12) the original r12 hoses may have to be replaced in perfroming an r134 conversion. The hoses in the TD are the same as in my D, which has the original r12, so they were not changed during the retrofit.

I suppose I could go back to r12.

I've seen mention of some on-line hvac exam that you have to take from OSHA or EPA to be certified to work on r12 systems and get r12 at reasonable prices. Anyone know any details about that? With two cars with ac problems, I might as well become competent at this and get the right tools.
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  #13  
Old 07-16-2003, 12:23 AM
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Your hoses are fine, no problems there (and R134 is bigger than R12, just lighter in molecular weight).

You do not have compressor engagement. If it's not running, even if you do manage to get the Freon in, it won't work. Check for a bad compressor clutch ground wire first, but it it is OK, check for contiuity through the clutch. If the coil is bad, no clutch. It can be replaced without discharging the AC, but I don't know if you really want to do it in the car or not, I've never tried.

You should get clutch engagement by jumpering battery voltage to the clutch wire -- watch to see if the front clutch plate starts to spin when you do.

I usually invert the first can of freon and allow the pressure in the can to drive the liquid freon into the AC, but I do this with the engine OFF. CCOT systems will tolerate liquid with no problem since the low pressue Schraeder will be on the accumlator, but MB uses an expansion valve system and they don't like liquid freon dumped into the compressor when it's running. One can will not leave liquid in the low pressure side, and I run it in on the high pressure side anyway.

I would stop where you are for the time being and fix the leak -- pull a good vacuum on the system, then shut off the line to the pump and watch the pressure -- you must hold at least 29" for at least 30 min, preferably indefinitely. I have the luxury of a very high capacity 100 mTorr pump, so I can get 30" of vac with even a moderate leak -- the normal small AC service pump will take half an hour or so to get to 29", mine will run down to 29 in about 30 sec. The key is having the system hold vac.

Check all the line connections -- a leak will leave residual refrigerant oil if it is very large -- this is how I knew the expansion vavle was leaking on the 300TE. I suspect the manifold gasket on the 300D -- this will be a big PITA since I cannot reach the screws on the inside with the compressor installed.

The normal conversion is to repair leaks, evacuate, and then add PAG oil and R134a. The mineral oil stays put (mostly in the compressor) while the PAG circulates with the Freon, providing properly lubrication. Ester oil will dissovle in the mineral oil, and if you do not have enough, will cause lubrication failure.

If you need to remove the compressor, drain the oil and flush the whole shebang, and replace the oil with ester oil, then charge with R134a. Charge ONLY to 85% of the R12 by weight, or it won't cool properly at low speeds.

Peter
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  #14  
Old 07-16-2003, 01:00 AM
Greg Martin
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psfred -
very useful advice.

Re evacuating the system/testing vacuum retention, is one of the venturi devices (as sold by ackits) sufficient? Supposed to develop 29in vaccuum. Another source insisted you need a pump good to 50 microns for proper results.

Re hoses again, from the Mastercool Auto AC Basic Service Manual, p 12,

"Because R-134a is composed of smaller molecules than R-12, the permeation of R-1341 through rubber hose is about double that of R-12, resulting in a faster loss of A/C charge. To correct this problem, nylon-lined or Nitrile Internal Barrier hoses are used. Internal barrier hoses use coupled hose connections instead of gear clamp fittings, which will not clamp the internal barrier hoses correctly...."

Just because this is published here doesn't mean it's correct, of course.

Now the blue mb high pressure hoses that I see on either side of the receiver/dryer have markings which may indicate they're ok for r-134 (I think the brand name is "nyl"-something), and they don't use gear clamp fittings, but I'm simply not sure that they're proper for r-134. I don't know what the recommendations are for a retrofit of this system.
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  #15  
Old 07-16-2003, 11:26 AM
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I have no problem getting to 29" of vacuum with the ackits venturi pump using a 5hp compressor.

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