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Cannot reach A/C high/low pressures



 
 
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  #1  
Old July 20th 05, 04:53 AM
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Default Cannot reach A/C high/low pressures

This is a 1990 Geo Metro. This car was previously converted to R134a.
Recently I replaced the compressor and dryer. I did everything by the
book. I flushed the system with isopropyl alcohol, replaced o-rings,
evacuated, oiled it and held a vacuum for several hours. There were no
leaks. I even purged it again with dry N2 and evacuated again.

Book calls for 1.1 lb of refrigirent (this was for R-12, so I was ready
to use only 1 lb of R134a). After putting in 1 lb of R134a, the
pressure did not reach the specified values (200/25 psi on the high/low
sides). I added some extra refrigirent, and then some more. The
pressure was still low. I ended up putting in twice the required amount
of refrigirent. But the pressure was still only 125/25 psi. I do not
hear or see any obvious signs leaks. Even if there were a leak,
wouldn't the pressure initially go up and then slowly come down? Where
is all the extra refrigerent going? The air is blowing a little cool,
but nowhere near where it should be. The high side tubes are hot, which
is a good sign. The compressor is turning over fine, and there are not
funny sounds. I am at a loss what to try next.

Any suggestions are appreciated.

Ads
  #2  
Old July 20th 05, 07:57 AM
Bruce Chang
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> wrote in message
ups.com...
> This is a 1990 Geo Metro. This car was previously converted to R134a.
> Recently I replaced the compressor and dryer. I did everything by the
> book. I flushed the system with isopropyl alcohol, replaced o-rings,
> evacuated, oiled it and held a vacuum for several hours. There were no
> leaks. I even purged it again with dry N2 and evacuated again.
>
> Book calls for 1.1 lb of refrigirent (this was for R-12, so I was ready
> to use only 1 lb of R134a). After putting in 1 lb of R134a, the
> pressure did not reach the specified values (200/25 psi on the high/low
> sides). I added some extra refrigirent, and then some more. The
> pressure was still low. I ended up putting in twice the required amount
> of refrigirent. But the pressure was still only 125/25 psi. I do not
> hear or see any obvious signs leaks. Even if there were a leak,
> wouldn't the pressure initially go up and then slowly come down? Where
> is all the extra refrigerent going? The air is blowing a little cool,
> but nowhere near where it should be. The high side tubes are hot, which
> is a good sign. The compressor is turning over fine, and there are not
> funny sounds. I am at a loss what to try next.
>
> Any suggestions are appreciated.
>


Sounds like your compressor isn't any good. Is the needle shaking or does
it hold steady? Overcharging the system would only make matters worse. Did
you happen to manually turn the compressor hub before letting the clutch
engage? As far as I understood, the amount of R134a compared to R12 should
be less. Something like 80% was it? Putting in 1 lb R134a compared to 1.1
lbs R12 is only 90%.


  #3  
Old July 20th 05, 01:00 PM
wws
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Bruce Chang wrote:
> > wrote in message
> ups.com...
>
>>This is a 1990 Geo Metro. This car was previously converted to R134a.
>>Recently I replaced the compressor and dryer. I did everything by the
>>book. I flushed the system with isopropyl alcohol, replaced o-rings,
>>evacuated, oiled it and held a vacuum for several hours. There were no
>>leaks. I even purged it again with dry N2 and evacuated again.
>>
>>Book calls for 1.1 lb of refrigirent (this was for R-12, so I was ready
>>to use only 1 lb of R134a). After putting in 1 lb of R134a, the
>>pressure did not reach the specified values (200/25 psi on the high/low
>>sides). I added some extra refrigirent, and then some more. The
>>pressure was still low. I ended up putting in twice the required amount
>>of refrigirent. But the pressure was still only 125/25 psi. I do not
>>hear or see any obvious signs leaks. Even if there were a leak,
>>wouldn't the pressure initially go up and then slowly come down? Where
>>is all the extra refrigerent going? The air is blowing a little cool,
>>but nowhere near where it should be. The high side tubes are hot, which
>>is a good sign. The compressor is turning over fine, and there are not
>>funny sounds. I am at a loss what to try next.
>>
>>Any suggestions are appreciated.
>>

>
>
> Sounds like your compressor isn't any good. Is the needle shaking or does
> it hold steady? Overcharging the system would only make matters worse. Did
> you happen to manually turn the compressor hub before letting the clutch
> engage? As far as I understood, the amount of R134a compared to R12 should
> be less. Something like 80% was it? Putting in 1 lb R134a compared to 1.1
> lbs R12 is only 90%.
>
>

Could be a leak, too.
THAT much 134a must be going somewhere.

wws
  #4  
Old July 20th 05, 01:04 PM
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Default

Yes, I manually turned the hub before letting it engage. Both pressures
appear to be steady. But I agree that the problem could be the
compressor. What I am afraid I might have done is put too much oil
into the compressor ports. I put about 3/4 oz of the oil into the
compressor and distributed the other 2 oz into the condensor and
evaporator. In any case, it does sound like the compressor has gone
bad. Any chance I can dismantle and repair it?

  #5  
Old July 20th 05, 01:30 PM
Comboverfish
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wrote:
> Yes, I manually turned the hub before letting it engage. Both pressures
> appear to be steady. But I agree that the problem could be the
> compressor. What I am afraid I might have done is put too much oil
> into the compressor ports. I put about 3/4 oz of the oil into the
> compressor and distributed the other 2 oz into the condensor and
> evaporator. In any case, it does sound like the compressor has gone
> bad.


I don't think that too much oil is the problem in your case, unless
previous repairs involved the continuous adding of unnecessary oil.
The compressor (a reman unit that you have no previous experience
using) could have had a stuck or bent high side reed valve from the
factory.

I like using Poly ester oil (what you used) in R134a coversions when it
is going to mix with mineral oil. I don't think the quantity or type
of oil is the cause of the problem here. The compressor probably came
with oil in it, but adding less than an ounce shouldn't spell disaster.

Any chance I can dismantle and repair it?

I guess your compressor DOESN'T have a warranty? If it does, then see
if the parts house will honor it -- this also may involve an inspection
for the type of damage -- lack of oil or too much oil for example can
cause compressor failures that are not covered by typical compressor
warranties. Unfortunately, if you got one with a bent reed valve, they
may still blame that on too much oil on startup. Make sure you explain
the preventative steps you took during installation.

If you really put TWO POUNDS of R134a in your system, then that is
dangerous! I'm not sure it would physically take that much liquid
freon on such a tiny system. Are you sure that you put in that much -
32 ounces? Cans are 12 oz each. If there was a rapid leak you would
be able to hear it. Make sure your high side gauge is accurate before
condemning the system. Put it on another working system to check. The
25 lbs low side isn't too far from normal on a mild day; it also
depends on the proximity of the fitting to the compressor.

Toyota MDT in MO

  #6  
Old July 20th 05, 08:23 PM
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Yes, I did put in 2 cans and then added about good part of a third can.
So that amounts to nearly 30 ounces. I did not hear any obvious leaks.
But I did hear momentary hissing from the low-side valve while I was
charging. It was such a short duration I doubt it could have leaked 1
lb of freon. I checked all the connections, and I don't see any sign of
oil seepage. One possibility is that a leak could be inside the
evaporator. But the system held a 30" vacuum for nearly 6 hours with no
drop at all. I would be surprised if there is a leak.

Unfortunately the compressor does not have warranty. It only had a
90-day warranty, and I kept it for almost a year before installing it.
If I can't fix the compressor myself, I will have to trash it and buy
another one. Is there a way to check the compressor operation without
charging with freon?

  #7  
Old July 21st 05, 01:21 PM
Comboverfish
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wrote:
> Yes, I did put in 2 cans and then added about good part of a third can.
> So that amounts to nearly 30 ounces. I did not hear any obvious leaks.
> But I did hear momentary hissing from the low-side valve while I was
> charging. It was such a short duration I doubt it could have leaked 1
> lb of freon. I checked all the connections, and I don't see any sign of
> oil seepage. One possibility is that a leak could be inside the
> evaporator. But the system held a 30" vacuum for nearly 6 hours with no
> drop at all. I would be surprised if there is a leak.
>
> Unfortunately the compressor does not have warranty. It only had a
> 90-day warranty, and I kept it for almost a year before installing it.
> If I can't fix the compressor myself, I will have to trash it and buy
> another one. Is there a way to check the compressor operation without
> charging with freon?


The noise you heard from the low side fitting may have just been the
rush of freon into your system during charging.

With a leak test of 6 hours, it is unlikely that you have a significant
leak, with the possible exception of your schrader valves (because the
gauges were hooked up to them at the time).

The best, easiest way to test a compressor is on the car with a
properly charged system. Evac and charge the system with the correct
weight of freon, probably .9 oz R134a. Double check your book figure
by looking in the engine compartment for an A/C label. Use 85% of the
R12 amount listed. 1.1 lbs sounds a little low even for a Metro; I
usually trust the car decal over a service book.

Finally, I would say that the compressor is bad based on your
pressures, but again, make sure your gauges are accurate.

Toyota MDT in MO

  #8  
Old July 21st 05, 04:15 PM
Bruce Chang
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Default


"Comboverfish" > wrote in message
oups.com...
>
>
> wrote:
>> Yes, I did put in 2 cans and then added about good part of a third can.
>> So that amounts to nearly 30 ounces. I did not hear any obvious leaks.
>> But I did hear momentary hissing from the low-side valve while I was
>> charging. It was such a short duration I doubt it could have leaked 1
>> lb of freon. I checked all the connections, and I don't see any sign of
>> oil seepage. One possibility is that a leak could be inside the
>> evaporator. But the system held a 30" vacuum for nearly 6 hours with no
>> drop at all. I would be surprised if there is a leak.
>>
>> Unfortunately the compressor does not have warranty. It only had a
>> 90-day warranty, and I kept it for almost a year before installing it.
>> If I can't fix the compressor myself, I will have to trash it and buy
>> another one. Is there a way to check the compressor operation without
>> charging with freon?

>
> The noise you heard from the low side fitting may have just been the
> rush of freon into your system during charging.
>
> With a leak test of 6 hours, it is unlikely that you have a significant
> leak, with the possible exception of your schrader valves (because the
> gauges were hooked up to them at the time).
>
> The best, easiest way to test a compressor is on the car with a
> properly charged system. Evac and charge the system with the correct
> weight of freon, probably .9 oz R134a. Double check your book figure
> by looking in the engine compartment for an A/C label. Use 85% of the
> R12 amount listed. 1.1 lbs sounds a little low even for a Metro; I
> usually trust the car decal over a service book.
>
> Finally, I would say that the compressor is bad based on your
> pressures, but again, make sure your gauges are accurate.
>
> Toyota MDT in MO
>


I'm pretty sure you already know this but you're using R134a and Freon
synonymously in your posts. It should be noted that Freon refers to R12.


  #9  
Old July 21st 05, 04:50 PM
Comboverfish
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Bruce Chang wrote:

> I'm pretty sure you already know this but you're using R134a and Freon
> synonymously in your posts. It should be noted that Freon refers to R12.


Dupont invented the name Freon to encompass several CFCs AFAIK. I use
the word freon just like I call colored wax sticks crayons.
'Refrigerant' takes longer to type esp. when you are using the word
alot!

Toyota MDT in MO

  #10  
Old July 21st 05, 05:08 PM
Bruce Chang
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Posts: n/a
Default


"Comboverfish" > wrote in message
oups.com...
>
>
> Bruce Chang wrote:
>
>> I'm pretty sure you already know this but you're using R134a and Freon
>> synonymously in your posts. It should be noted that Freon refers to R12.

>
> Dupont invented the name Freon to encompass several CFCs AFAIK. I use
> the word freon just like I call colored wax sticks crayons.
> 'Refrigerant' takes longer to type esp. when you are using the word
> alot!
>


Then I guess I should have said, "R134a is not Freon". I agree that it
takes a lot longer to type refridgerant but I didn't want to perpetuate the
misconception that all refridgerants can be referred to as Freon.

If you're using Freon like you use the word crayon, then you should realize
that crayons aren't trademarked by Crayola. A crayon IS a colored wax
stick. I think you meant something like "band-aid" or "Xerox" or "Kleenex".
That was my point in mentioning the use of Freon as a generic term for
refridgerant when it doesn't encompass all refridgerants, in particular
R134a.


 




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