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  #1  
Old 07-29-2003, 10:23 AM
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All of the AC facts in one place.. Divine intervention needed???

I know some of you are tired of reading AC posts from me, and quite frankly, I am too..

My system was originaly charged with some kind of blend of r-12, and 134a.. Readings were 400/50 @ 1500 RPM..I evacuated, and completely flushed the system clean as a whistle..

I did not replace the expansion valve that has R-134a stamped on the side. I was told by two different sources that it would work fine with r-12..

I put everythind back together, with new o-rings, correct amount of oil, new drier, and charged to the 2.9 lbs specified for the w-126 chassis with r-12.

The condenser fan is blowing.

The heater hose is blocked off with a shutoff valve.

THe compressor runs quietly..

At idle readings

ambient temp 85
Low side 45
high side 180
vent temps about 70
Low side return hose is cool, but not cold...

at 2000 rpm or so

low side 33
high side 250-275
vent temps low 60s or so
low side return hose is cooler than before, but still not ice cold

For reasons that escape me.. The system is simplty NOT making the evaporator cold enough to bring the vent temps down..

Looks like I'm down to two or three things.. Either there is something wrong with the compressor, the expansion valve, or the 2.9 lbs listed is overcharging the system???

Is it time for me to just take it to the AC shop??? HELP.....

Sincerley,
Jay Davenport

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  #2  
Old 07-29-2003, 11:40 AM
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OK, I'll give it a shot.

Compressor looks good to me. If it's quiet and capable of generating 275 on the high side, it's definately doing some compressing. No problems there.

I can think of three possible problems.

Is the high side restricted, limiting the flow of refrigerant to the evaporator. Feel the high side line - it should be hot all the way to the expansion valve. If it turns cold at a point before the expansion valve, you've found the problem.

Could be a bad expansion valve. I usually replaced these on spec when the system is apart, they're only 25 bucks or so.

Any possibility the evaporator is restricted by leaves or dirt in the air path? If part of the evaporator is blocked it just can't extract the required number of BTUs from the air flowing over it. Result - slightly cool, muggy air.

That's all that comes to mind. The high side pressures look good, the low side look OK at idle, but is higher than I like to see at 1500 RPM.

- JimY
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  #3  
Old 07-29-2003, 11:57 AM
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I flused the entire system, so I know there are no blockages.

I'm an idiot for not replacing the expansion valve while I had it in my hand.. Oh well, it will be easier this time, since I've already made my special tool

I agree that the compressor compresses.. It was making 400 psi with the blend that was in it..

I seriously doubt that the evap is restricted.. I have lots of air flow, and it's a very clean car, even in all the nooks and crannies under the hood.. The evap is not getting very cold anyway..

I guess there is nothing left to do , but try another expansion valve...
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  #4  
Old 07-29-2003, 06:43 PM
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Location: Matthews, NC
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I think your problem is overcharged. I have a 84 500SEL which I had many problems trying to get it to cool.
I tried everything (like you) and nothing seemed to work. Now let me be truthful and say I was using R134. I then tried Freeze 12 one time and things were worse. Flushed everything again, replaced the dryer, then put in 1.5 lbs of r134. I set the RPM to 1500. Checked center vent temp after about 2 or 3 min. I forget what it was, but it didn't matter (as you will understand in a moment.). I then added 2 ozs and again watched the center temp. It droped 2 or 3 degrees. Again added 2 ozs. Again temp droped. I kept doing this until the 2 ozs didn't drop the temp anymore. I'm sorry that I can't remember exactly how much I put in the system, but It doesn't matter. Now the A/C system works great with the R134. I will agree it is not quite as cold at idle as it may be with R12 but but when moving it works just as good.
Going about 50 or 60 mph the center duct temp is about 42 degrees and at Idle it goes up to about 48 or so.
If you try this method, you will need a good scale to mesure the amount of freeon put in each time and watch the guages very closely to make sure pressures dont go to high.
I have used this method on several other conversions and all are working great.

Now I am sure the same method will work with R12.
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  #5  
Old 07-29-2003, 09:12 PM
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Several people have said that it might be overcharged.. That's certainly an easy place to start, by backing some out, and see if it gets better.. Sure seems strange though. The label says clearly w-126 2.9 lbs.. Maybe i'll back it out to two pounds, and go up from there..

I sure wish the new drier I bought from ACKITS had site glass on it..

Time to put it on the r-12 machine and play with it.. It's good having friends in the right places.. But sure don't want to wear out my welcome..
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  #6  
Old 07-30-2003, 07:08 AM
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Seems I did see a techinical bullitin about the amount of r12 to put in the 126. It was after I converted my system so I didn't pay much attention to it. I will try to find it today.

Good luck
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  #7  
Old 07-30-2003, 08:30 AM
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Quote:
Originally posted by pmckechnie
Seems I did see a techinical bullitin about the amount of r12 to put in the 126. It was after I converted my system so I didn't pay much attention to it. I will try to find it today.

Good luck
I would definitely appreciate that..
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  #8  
Old 07-30-2003, 11:45 AM
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It looks like it could be overcharged based on your pressures. Low side should be lower than that (around 29 psi) at 2000rpm, as should the high side (more like 180 or 190psi at 2000rpm). Idle pressures don't tell you much. If it isn't overcharged, then I would say for sure you need to replace the expansion valve. But once you have proper low side pressure, you should be getting low 40 degree vent temps.

GregS
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  #9  
Old 07-30-2003, 11:56 AM
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Location: Florida / N.H.
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134 expansion valves are designed for higher pressure than R12 .
It is my understanding that one can get away with a R12 valve when going to 134, but not going to R12 w/134 valve..
???????????????
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  #10  
Old 07-30-2003, 12:05 PM
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Interesting... Arthur.. Very interesting.. I wish I could find out more about that..
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  #11  
Old 07-30-2003, 12:12 PM
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Quote:
Originally posted by jay3000
Interesting... Arthur.. Very interesting.. I wish I could find out more about that..
Maybe someone with auto a/c expertise will have specs on that ..
I was more in to Domestic Refrigeration in an earlier life, so I am not hip on 134 specs/parameters...
I am from the R12/22 generation when a 30 lb. tank cost $18
and guys used it to blow out condensors !!!!
....ouch...
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  #12  
Old 08-02-2003, 01:57 PM
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JAY3000

I'm sorry it took me so long to find the tech bulleten I mentioned but work has been so hectic this past week that...........
I did find it, but it was published in 1985 so it wouldn't actually apply to your car. I did check it anyway and it says to use 2.866 lbs (45.8 oz)(1.3kg) of freon so you were about right. However, I have seen quite a few cars that needed a little more, or a little less to work correctly.
Going by the pressures you were getting, I believe you may need less than normal.

Have you tried anything sense your last post?
Let us know.
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  #13  
Old 08-02-2003, 02:09 PM
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Well I disagree.

The pressures don't look like a system that is overcharged. The high side is low if anything. The problem might not be refrigeration, but the low side ain't all that great.

It absolutely doesn't look like a restricted system as the low side would at least look better if there was a restriction.

There is a possibility of a too open expansion valve but the calibration for 134 should restrict the flow if anything, not open it.

The 126 car can be one of the worst for internal airflow blockages through the evaporator and the lack of control by the recirc doors will kill 10-15degrees of duct temp. The recirc is two stage. The first stage causes about 70% of the air to be recirc and is set in place whenever the AC is on. Left in the 100% vent condition the air will be 10-15degrees warmer.
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  #14  
Old 08-02-2003, 03:24 PM
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Steve,
Actually I agree with you about it possibly not being a refrigeration system problem at all. You, I, and others have said that this is too high and this or that is to low, but from what I have seen, an R12 system should be perty cold at these pressures. The only refrigeration problem I could think of is possible there is some air in the system which I have seen happen, the pressures look good enough to cool but actually will not cool at all.
Now back to your views on the air flow in the older 126 cars. You are 100% correct. When I first started trying to get my old 1984 500 SEL to cool, I found several problems. First the recuitulation problem. Bad vacumn elements. Modified the system to get 100% anytime any amount was called for. Second the deverter flat didn't change when it should (By the way, what is the deverter valve for? It doesn't seem to do much but it did help after it was repaired). Third, I removed the blower motor and looked at the evaperator core (using mirrows) and saw a lot of dirt, leaves, etc. It was nasty. After thinking about it, the core gets wet with condensation, dust comes in and stickes to the core and changes into mud. This would act as insulation. I made a small spray nozzle from a small piece of metal pipe with a 90 deg bend at the very end. Got is hooked to a water hose and used it along with flashlights and mirrows and washed the core. The water and dirt ran out the drain hoses. It was terribly dirty. I washed until it ran out clean. That one thing helped by about 5 degrees.
So it could be part of Jay's problem. Also on these 126 cars if the monovalve starts going bad can't it also cause his problem?
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  #15  
Old 08-03-2003, 08:16 PM
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Yeah.. I'm still out here.. Been at the beach for a few days. Took the Buick.. Although I installed a monovalve repair kit about 6 months ago I went the extra step and installed a manual shutoff valve in the heater hose. So hopefully there is no flow through the heater core at all.

This system is simply not getting very cold.. At least not while the car is stationary.. The low side hose as it exits the firewall is cold enough to sweat, but that's about it.. When you put your hand on it it's not very cold..It should be real close to being frosty?? Right???

It seems that I really don't have any option at this point but to recover what is in there.. Put in a known correct expansion valve, and start over...

Anyone see a different option??? Maybe the expansion valve I have is stuck at some partially open position??

I'm still stumped...How do I manually close off the outside air????

Jay

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