A/C troubleshooting

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gull
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A/C troubleshooting

Post by gull » Mon Jul 27, 2009 6:39 pm

My Cabby has a non-working A/C system. It appears to be complete and in good shape, but when I move the selector to the A/C settings the compressor doesn't engage. The fuses are good. I was never too interested in it before, but the recent hot weather, a planned trip to eastern Washington, and the difficulty in keeping the windows defogged last winter, have made me think maybe I ought to at least take a shot at figuring out what's wrong with it.

Does anyone know where there's a good troubleshooting guide for the A/C system in these cars? At very least I'd like to find and jumper the low pressure cut-out switch so I can figure out if it has an electrical fault or if it's just low on Freon.
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Re: A/C troubleshooting

Post by Briano1234 » Mon Jul 27, 2009 9:01 pm

There are 2 switches on the hoses prior to the Dryer...... One is the low pressure switch the other is the high pressure switch.

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It is easier to check to see if the compressor turns, by with the engine running, putting 12V to the hot side of the connector. Also check to see that the Ground wire is attached to the connector and to the alternator.
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Re: A/C troubleshooting

Post by Calimus » Tue Jul 28, 2009 11:42 am

Also keep in mind that the electric clutch will not engage if there is no pressure in the AC system. So, if the system has been drained or all the coolent has leaked out, the system is smart enough not to turn activate the clutch when you switch things on.
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Re: A/C troubleshooting

Post by gull » Tue Jul 28, 2009 12:45 pm

Yeah, that's what I'm trying to sort out by finding the low pressure switch. I figure if the compressor engages when I jumper it, then the problem is as you describe -- no Freon in the system. If the compressor doesn't engage, then I have an electrical problem elsewhere.

My gut feeling is that all the Freon has leaked out over the last 20 years, which would kind of suck since it's an R-12 system. It may not be cost effective to repair it if that's the case.
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Re: A/C troubleshooting

Post by Briano1234 » Tue Jul 28, 2009 3:40 pm

gull wrote:Yeah, that's what I'm trying to sort out by finding the low pressure switch. I figure if the compressor engages when I jumper it, then the problem is as you describe -- no Freon in the system. If the compressor doesn't engage, then I have an electrical problem elsewhere.

My gut feeling is that all the Freon has leaked out over the last 20 years, which would kind of suck since it's an R-12 system. It may not be cost effective to repair it if that's the case.
Yes it does have a negative air displacement ratio to have the a/c system not work. But that is why I suggest to Jump +12vdc to the compressor while the engine is running. This will tell you that the clutch and compressor are good.

You can buy a 134a conversion kit, but in honesty you need to drain the old oil out of the compressor and the receiver/dryer and use fresh 134a pag oil
then you can recharge your system with 134A while not as effective as R12 IMHO it does work... and is available to the masses without a license, although I imagine that with the current glut of liberal eco-nazi's in office that it will change.

I have converted my bunnies after getting them, the a/c on most didn't work or they needed new condensers.



From a earlier thread.....

How I converted my a/c to r134a
As it is getting close to the time when folks need a/c work....here is a running dialogue that I had with Thomas Covenant, on a different forum.

Thomas it was really rather easy. I took the receiver/dryer out,
poured out the oil in it then I took the compressor off and poured
the oil out of it.

Filled the compressor with the proper quantity of pag oil, Replaced
all the o-rings that I broke the connectors on with nitrite rings.

Replaced the Condenser (salvaged from a wrecking yard, at 15 bucks
easier to take.

Then (here is where the nay-sayers are going to balk.) Placed on
the converter fittings and Placed one can of freon (r134a) in the
car.

Then I went to the high pressure side of the condenser (engine not
running yet) and loosed the fitting till freon rushed out, for 10 seconds
then re-tightened. ( be careful not to get frost bite ). Wait 2 minutes for the
system to equalize. I started thecar, on the suction side placed a o-ring sealer in it,
then added a can or 134a. Turned on the a/c and it engaged the
compressor and sucked that can dry. I then topped it off with the
proper amount of r134a that it used for r12. Now the nay sayers
will tell you to draw vacuum, but I am a cheap bastard ( cost
effective) and was taught shade tree a/c from a friend. Bleeding
the high pressure side forces the high side to have hi pressure,
the low suction side then has low pressure, and you have then purged
all the lines of air...cool huh? So that when you kick it on, it
will suck in that can of freon like it should.....

Buying the kits will get you half the way there, but on my eagle I
had to use a high pressure adapter on the low side (only fitting
that would work) then buy a manifold kit and it comes with an
adapter and a gauge that connects to the High connector and then
allows you to place a can of Freon on it. The Two biggest problems
that I have seen happen with those kits, is that the compressor gets
too much oil. Draining the oil out of the Dryer, and the Compressor
and re-filling it with the proper amount of Pag oil is paramount to
getting a quiet and smooth running operation. I never buy the oil
charge, as I have filled the thing with the correct amount. Dupont
makes a Yellow can of leak detector, that you can see with uv
light. Most of the Cars I converted were because of a leaking
compressor 2 holed condenser and a compressor that locked up.

now for the ECO-Nazi's You should have your freon r12 sucked out by
a quality shop...as it has been known to damage the O-Zone ( my Ass)
layer. Like cow Flatuance, Mt Penetobo, Mt St. Helens didn't
either, but I didn't see the Eco-Nazi's fining Mother Nature. But
if your system is devoid of r12 by a broken condenser, loose fitting
(wink wink)then there is no problem with inserting the r134a instead
of r12, just remember that you need to drain all the oil out you
can. Run the a/c at max and if the lines don't sweat after a few
minutes then you need more freon, the other side of the coin is that
when the line starts sweating, your system has enough freon to do
the job. But personally I prefer the weighted method.

You will get all kinds of nay sayers and God-who-knows-it-alls, but
these are the steps that I followed, and they worked for me.




The Low pressure side where I put the convertor on.

Image

The receiver dryer, that I removed to drain all the oil.
Under the washer jug

Image



Closeup of the low pressure side
Image


pic of the High pressure side I bleed the 134a on it is to the front of the radiator hose nipple.....

Image

pressure test

low side 15 to 30
High side 150-270 up to 84
high side 150-210 from 85 up to 93

Oil
r209 compressor 79-81 10.0
sc209 compressor 79-81 8.0
Sankyo compressor 79-81 6.0

82-84
sankyo/sanden 10.0
york sc-209 8.0

85-89 6.0

90-93 4.8

Refridgerant

80 2.06 pounds
81-84 2.0
85-91 2.5
92-93 2.06

I would assume that 92's lower poundage is due to r134 being installed.....but I can't verify that for a fact.

I went by the weight of the can for the total poundage that I was putting in then verified it by pressure/sweating test.
Last edited by Briano1234 on Tue Jun 04, 2013 9:08 pm, edited 1 time in total.
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Re: A/C troubleshooting

Post by kamzcab86 » Tue Jul 28, 2009 5:09 pm

gull wrote:My gut feeling is that all the Freon has leaked out over the last 20 years, which would kind of suck since it's an R-12 system. It may not be cost effective to repair it if that's the case.
My Cab has been slowly blowing warmer air over time and, now, is no longer blowing cold air (good thing since it's only supposed to be 115°F today and I'm out of ice cream... and to top it off, the Jetta's HVAC blower control unit quit! :banghead: ) and I'm guessing it needs a re-charge (last re-charge was over 10 years ago). It too is still R-12, and several shops around Phoenix still supply R-12 (woohoo!). My Cab doesn't care to lose her religion, so rather than converting, she'll be re-baptized with R-12. How much it'll cost, don't know yet. So, if yours is indeed out of freon, you might want to check some shops in your area about re-charging with R-12; if no one has it, or it costs a fortune, might be time to convert.

I was going to follow Brian's how-to and convert mine, but after finding out I can still get R-12 put in the car, well... to hell with the environment! :mrgreen:

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Re: A/C troubleshooting

Post by gull » Tue Jul 28, 2009 5:30 pm

Thanks for the info. I really would prefer to avoid an R-134a conversion; my past experience is that converted systems don't perform well and the R-12 hoses leak R-134a like a sieve.

ES-12 seems to have a lot of fans. I may consider converting to that if it looks like I just need a recharge.
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Re: A/C troubleshooting

Post by gull » Sat Aug 29, 2009 5:20 pm

OK, finally got around to working on this. (It's been a busy month.) First thing I discovered was that the ground wire from the A/C compressor to the alternator was loose. Fixed that, still no go. Then I jumped across the switch with the two green wires (I assume this is the low pressure cut-out switch) and the compressor engaged. I didn't see anything in the sight glass.

I'm guessing this means the system needs a recharge.
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Re: A/C troubleshooting

Post by SoCal_Cabby » Tue Sep 01, 2009 5:43 am

if you are low on freon the A/C compressor will not engage...
if you are low on freon then you have a leak....

check those first then trouble shoot from there.


i wish i was still up there to help you...i used to live in auburn, then moved to federal way then back to cali

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Re: A/C troubleshooting

Post by gull » Tue Sep 01, 2009 12:51 pm

Yeah, I'm sure it has a leak. Which is probably why the PO never fixed it. Given how rarely it really gets hot here, I don't think it's worth fixing at this point.
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Re: A/C troubleshooting

Post by GreenCabbie » Fri Aug 03, 2012 6:52 pm

:? My ac is not working due to many reasons. Some of my mistakes I think but don't really know. I followed all of the advice to evacuate the system and then shut the Multivalves off to see if it would not loose pressure for 1/2 hour. It passed.

So I loaded in 18 oz of R134a freon. The clutch on the compressor did not engage so I followed your advice to jump it from the battery to the low side pressure switch and clutch and compressor came on. Earlier I had asked how much R134a to put since the R12 system capacity was 40 oz the suggestion was about the same. So I added 12 more oz. My readings are no where near where yours are.

My low side is 100 psi. My high side is 100 psi. There is no cooling going on and the clutch on the compressor only works if I jumper it.

Should I start over? Or are there other problems lurking? I have the compressor clutch back on the ac thermostat. I could go back to the ac cutoff switch I still have in the dash. To be able to not have to jumper it.

:?:

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Re: A/C troubleshooting

Post by Briano1234 » Fri Aug 03, 2012 8:32 pm

The ac clutch is picked by placing the selector in the blue or defrost setting. There is a switch on the right side of the controls, that depresses for those, and releases for the two no a/c setting. This is where the ac/cutout is placed.

There is the Thermoswitch on the left side that has a mercury tube that goes in to the evaporator core on the right side of the heater box. It turns off the system if there is a frozen or ice build up on the evap core (this is what cycles the a/c on cars as you are running.)

There is the Low pressure cut out that is on the dryer near the windshield washer jug.

There is the a/c compressor relay in the fuse box.

I would think that your relay may be giving you grief.

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Re: A/C troubleshooting

Post by GreenCabbie » Sun Aug 05, 2012 3:26 pm

Thanks as always Briano. I went to followup on your advice by looking at the relays. The DIY relay replacement showed relay no 5 as the a/c relay. Was this for another model than a 1993 VW Cab.

My car shows a relay no 13. Which I happen to have an extra relay 13. I plugged it in and neither worked. So is it relay 5 or 13 to buy new.

So trying to make this easy for myself to understand I thought.

I reconnected the ac cutoff switch to by pass the ac thermostat. And the number 14 blower fuse blew. Something must be shorting between AC cutoff switch fuse and that number 14 blower fuse or shorting downstream of the ac cutoff switch.

I am wondering if I use the ac cut out switch and set a big jumper to go to the low press refrigerant switch if I can get the compressor clutch to come on. Maybe the short is in the other direction from the relay. Last time I jumped from the battery to the low pressure switch the clutch on the compressor started. Is there away to test the low and high pressure ac refrigerant switches?

What do you think? :idea:

Thanks

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Re: A/C troubleshooting

Post by Briano1234 » Sun Aug 05, 2012 5:47 pm

GreenCabbie wrote:Thanks as always Briano. I went to followup on your advice by looking at the relays. The DIY relay replacement showed relay no 5 as the a/c relay. Was this for another model than a 1993 VW Cab.

My car shows a relay no 13. Which I happen to have an extra relay 13. I plugged it in and neither worked. So is it relay 5 or 13 to buy new.

So trying to make this easy for myself to understand I thought.

I reconnected the ac cutoff switch to by pass the ac thermostat. And the number 14 blower fuse blew. Something must be shorting between AC cutoff switch fuse and that number 14 blower fuse or shorting downstream of the ac cutoff switch.

I am wondering if I use the ac cut out switch and set a big jumper to go to the low press refrigerant switch if I can get the compressor clutch to come on. Maybe the short is in the other direction from the relay. Last time I jumped from the battery to the low pressure switch the clutch on the compressor started. Is there away to test the low and high pressure ac refrigerant switches?

What do you think? :idea:

Thanks

GreenCabbie
The high switch is normally open. so that is out of the loop.

If you apply 12 to the low pressure switch, and the compressor comes on then it is a switch issue or low pressure. So that would leave me to believe that your relay is toasted...if the car has pressure.

Now, the relays are marked funny. You have to use the diagram.
Image

The green fuse above is the a/c fuse.
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Re: A/C troubleshooting

Post by GreenCabbie » Sun Aug 05, 2012 7:42 pm

Now this picture makes sense. No 13 is the relay I have. What keeps the relay from going bad again if I plug in a new one?

The fuse that blows is no. 14. Not the 30 amp above the no. 13 relay. Why would that be?

I guess my next steps would be.

1.Buy a new no 13 relay or a used one if I can find one. Is there a place that tests these relays? Do you have a trusted source to purchase one.
2.Install it.
3.The 40 oz of 134a I put in is still somewhere in the system. I haven't seen it leak anywhere.
4.If I start the clutch on the compressor it should pressurize the system. I would like to use the ac cutoff switch but if it trips the no. 14 breaker I may have to put it back on the air distributor and try it that way.
If that doesn't work dare I jumper the compressor again?
5.The high pressure cutoff valve should turn off the compressor when it is activated. (200 psi?) My last run of the compressor couldn't get it to 105 psi on the high side.
6.If it doesn't .......how would I test the low pressure ac refrigerant switch? Since it may be bad.

Did I miss anything?


Do you have a photo of which is the low pressure switch and which is the high pressure switch?
The last time I started the clutch on the compressor I jumpered from the positive terminal on the battery to the first pressure cutoff valve nearest the condenser. Using the second female plug in off the terminal . It started the clutch and ran for about 10 minutes. Creating a low side pressure of 100 and High side pressure of 105.

I wonder with the ac cutoff wires used for the switch to bypass the ac thermostat what keeps the evaporator from freezing up?

The way I read the wiring diagram if you have the compressor on too long you could freeze the evaporator up because the mercury tube is disconnected since you moved the ac cutoff wires over to the cutout switch or am I reading more into this than I see. Is the mercury tube connected elsewhere to protect the evaporator.

I am certainly learning alot the hard way and appreciate you patience in coaching me through this.

Can't thank you enough for all you time, Briano :)

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