a/c

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  #1  
Old 08-06-02, 09:22 PM
biker50
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a/c

Would anyone help with advice on replacing an a/c compressor? Vehicle is '89 Voyager, 2.5 Turbo. When the unit wasn't cooling I changed it over to 134a and added dye to check for leaks. Subsequently it ran quite hot and the clutch appeared to come off after bolts melted (no kidding). I have to do this myself as there's no way I can spend the bucks on this to have it done by a shop. If there are metal filings in the lines how can I flush the system? I am wondering about adding oil - I understand I should dump some into the compressor and turn it by hand before closing the system. Should I put all the oil in at this time and will oil be pulled out when I have the vacuum pulled on the system? I do plan to replace the accumulator and have been told that if all of this is being done it makes sense to also replace the expansion valve. All advice will be happily received. Thanks.
 
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  #2  
Old 08-06-02, 11:23 PM
knuckles
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These vans *can* be converted to R-134a, but it's a tricky process. You have to get the charge EXACTLY right or you'll have a)no cooling or b)compressor death.

You ended up with b, which means you overcharged w/ R-134a when you retrofitted.

Here's my suggestion.

1. Go to an a/c shop & have them recover the existing refrigerant from your system.

2. Remove the compressor. Drain the oil from the old compressor in to a graduated container (a cheap plastic measuring cup will work perfectly). Note the amount of oil removed.

3. Flush the condensor with an approved flush solvent.

4. Remove the expansion valve & flush the evaporator & a/c hoses with approved flush solvent. After flushing, add 2 oz. of ESTER oil to the condensor inlet & 1 oz. to the evaporator inlet.

5. Install a new expansion valve.

6. Inspect a/c lines for damage or leaks. Replace as necessary.

7. Install a NEW, not reman. compressor. The OEM Chrysler compressor tends to wear/bend the clutch hub. This issue is not addressed during rebuilding & it leads to a dragging a/c clutch & early clutch failure.

8. Add at least 4 oz. of ESTER oil to the new compressor inlet. Turn the compressor shaft several times to distribute the oil. If you removed more than 4oz. of oil from the old compressor, add oil until the amount of oil removed from the old compressor equals the amount of oil added to the new compressor. For example, if you removed 6 oz. of oil from the old compressor, add 6 oz. to the new compressor. Again, make sure you rotate the compressor shaft several times to distribute the oil.

9. Evacuate the system & check for leaks.

10. Begin charging w/ R-134a. Add 1 12 oz. can for starters. With the engine running at about 1500-2000 RPM, note the system pressures & duct temps. Continue adding refrigerant 1 oz. at a time until the duct temps are good (40 degrees or so) and your pressures are acceptable.

'Acceptable' means 19-30 psi on the low side & no higher than 275 on the high side. Pressures will fluctuate with ambient temps. Colder temps=lower pressures & vice versa.

Make a note of the amount of refrigerant added. Write this down on the light blue retrofit label you should have already pasted under the hood.


You can buy a flush gun and solvent from any decent parts store. If you can't find one locally, try www.ontool.com or http://www.acsource.com/subcatmfgpro...4&1=256&2=1077
 
  #3  
Old 08-07-02, 05:47 AM
Joe_F
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Thumbs up

I agree with Knuckles...good job, very detailed....additions:

1) Change all your O-rings in the system. They are likely dust on an old Mopar heap like this.

2) Also change the A/C hoses. Chrysler used for whatever reason steel/metal manifold lines which turn to dust and are the source of leaks. Newer hoses are barrier type hoses and will withstand the R134A better.

3) Change the dryer too, if you haven't already done it.

4) A new Chrysler compressor is probably big bucks and all this work will exceed the value of the truck . I believe that Mopar makes a good rebuilt compressor, which would address the problem that Knuckles states in the aftermarket rebuilds. On my friend's 1991 Shadow, I can remember as far back as 1992 shimming the compressor with a feeler gauge to "fix" it. Lasted 6 years and we did it again later on. Crappy system, subsequently my friend ripped out the entire A/C system. Lol.

Other than that, Knuckles gave you excellent advice that is right on. Couldn't have said it bettter myself . Good job Knuckles!
 
  #4  
Old 08-08-02, 05:37 AM
Dan Meyer
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I've not had any experience with converting Voyager's over to R-134a but on the cars I have converted, I've aways dropped down one size on the orifice tube. What do you think???
 
  #5  
Old 08-08-02, 06:53 AM
Joe_F
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Just use what the manufacturer recommends for the conversion by part # and it should be fine.
 
  #6  
Old 08-08-02, 12:01 PM
biker50
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another question

How do I add 1 oz. at a time? The guy at the parts store said that the charge should be 84% of the R-12 - is that right and can I just start with that?
 
  #7  
Old 08-08-02, 07:38 PM
knuckles
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I've aways dropped down one size on the orifice tube. What do you think???
This car does not use an orifice tube. It uses an expansion valve instead. R-134a calibrated aftermarket expansion valves are available & one should be used in this case.

How do I add 1 oz. at a time? The guy at the parts store said that the charge should be 84% of the R-12 - is that right and can I just start with that?
You add 1 oz. at a time with a charging scale or a charging station. You *may* be able to rent or borrow one. If not, simply crack the low side valve on your gauges for a second or two, then close it. Allow the pressures to stabilize & check the duct temp. Keep adding in small increments until you get good cooling and acceptable pressures.

80-85% is a rule of thumb & it's not necessarily accurate. Each conversion will vary. It's far better to under charge than it is to overcharge as you've already found out the hard way.

I like to start w/ one 12 oz. can & work my way up from there.

I converted a 1981 Mercedes 300D just this week. OEM specs call for 1300g of R-12 (nearly 48oz. or 4 12 oz. cans). I found the best R-134a charge to be roughly 50% of the R-12 charge (2 12oz. cans). I achieved a 38 degree outlet temp & good system pressures with this charge.
 
  #8  
Old 08-09-02, 01:23 PM
Dan Meyer
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Isn't an expansion valve and a orifice tube one and the same thing?? Converts high pressure liquid to low pressure liquid. In as much as R-134a has a smaller molecular structure than R-12, the pressure/temperature relationship is different. (a reason for using 70-80% of R-134a over the original amount of R-12). Therefore, I think that it would be prudent to be sure of the orifice size (to help with cooling) before putting the system back together. Just a suggestion..
 
  #9  
Old 08-09-02, 01:27 PM
Joe_F
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Stick with what the OEM or that aftermarket company recommends for the conversion, not deviating and you should be fine .
 
  #10  
Old 08-09-02, 06:50 PM
knuckles
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Arrow Expansion valve vs. orifice tube

Isn't an expansion valve and a orifice tube one and the same thing??

In a word, no.

In many words....


An expansion valve and an orifice tube achieve the same result, but they are not the same thing.

An orifice tube is just that. It's a tube with a precision hole in it surrounded by an inlet & outlet screen. Orifice tubes are most often found in cycling clutch (many GM & Ford) applications.

These systems use a low pressure cycling switch in the suction line or accumulator near the evaporator. The switch shuts off the power to the compressor clutch to control evaporator temperature/pressure.

An expansion valve is a variable orifice. It uses a sensing bulb (internal in this application, external on other applications) in the suction line to determine evaporator temperature. The sensing bulb forces the expansion valve to move (open or closed) based on the evaporator temperature. Too cold forces the valve closed. Too warm opens the valve. These systems do not cycle the compressor clutch in normal operation, but they usually have a low pressure cut-off switch in the suction line to prevent compressor damage if the refrigerant charge is lost.
 
  #11  
Old 08-10-02, 06:18 AM
Joe_F
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Another way to look at it:

If you've ever seen an old cold control (thermostat) on a refrigerator, they have this type of capillary tube/sensing bulb Knuckles is talking about.

When I changed the cold control on my mother's fridge a few years ago, this is what it had .
 
  #12  
Old 08-11-02, 11:36 AM
Dan Meyer
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OK, that explains it. I've only done work on GM and Ford A/C's . If a Chrysler product comes along I'll have some idea what to look for.
 
  #13  
Old 08-12-02, 10:26 PM
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On my old Raggedy Suburban I've got an orifice tube on the front air and an expansion valve on the rear air. Both worked great for a 134 conversion.
Any ideas (or guesses) why GM would put both different flow controls on one system?
 
  #14  
Old 08-12-02, 10:36 PM
knuckles
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Post educated guess

I'm by no means an engineer, but I can offer an educated guess.

1. The fixed orifice tube was the standard a/c system on older GM cars & trucks.

2. The rear a/c unit was optional equipment, designed to work in conjuction w/ the 'default' front a/c system.

3. A fixed orifice tube in the rear would flow a constant amount of liquid refrigerant whether the rear a/c was in use or not. This would diminish FRONT a/c performance. An expansion valve will close when the sensing bulb detects a cold evaporator. This would improve FRONT a/c performance when the rear a/c was not in use.

Sound reasonable?
 
  #15  
Old 08-12-02, 11:06 PM
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That seems to make sense. When you "turn on" the rear AC you're really only turning on the blower motor. I guess that if the blower is off there is no heat transfer so the valve will be closed for longer periods of time. I'll have to check this out the next time I have to pull the cowling off back there.
 
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