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Old 06-01-2012, 07:44 PM
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Not to thread jack, but my85 a/c system has a problem. This could be related to the post title. The clutch and compressor are good, and plumbing has been converted to 134a. Most of the O rings and a few fittings were replaced. Liquid teflon was used on some aluminum connections they were soft and didnt know how tight to stretch the thread. Even replaced the schrader valves in the system. My problem is a leak. No dye shows anywhere. After shut down you can hear a hiss directly after the compressor is shut down. I believe since no dye is showing it might be sucking in on the low side. I have been over it with a bubble solution and spray bottle. Shouldd I replace the low side o rings again, or could the fitting not be sealing with the liquid teflon?

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Old 06-01-2012, 07:56 PM
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Quote:
Originally Posted by spinn
Not to thread jack, but my85 a/c system has a problem. This could be related to the post title. The clutch and compressor are good, and plumbing has been converted to 134a. Most of the O rings and a few fittings were replaced. Liquid teflon was used on some aluminum connections they were soft and didnt know how tight to stretch the thread. Even replaced the schrader valves in the system. My problem is a leak. No dye shows anywhere. After shut down you can hear a hiss directly after the compressor is shut down. I believe since no dye is showing it might be sucking in on the low side. I have been over it with a bubble solution and spray bottle. Shouldd I replace the low side o rings again, or could the fitting not be sealing with the liquid teflon?

Thanks
The hiss you hear is the pressure equalizing inside the system after the compressor stops running, its normal.
No teflon or anti seize should be used on threads of fittings.
O rings are what seals the system.
Look for traces of refrigerant oil, as that would be indicative of a leak. The freon evaporates but oil stays behind.
If you dont see any oil or dye anywhere, chances are the evap is your leak.
Look in the drain tube for the evap, trces of dye should be inside the tube if it is leaking. Also a lot of GM models, you can pull the blower resistor and look down inside for the trace of dye on the evap core. In that case just remember the resistor is on the air intake side so you may not see much dye, but some should be visible as the system leaks when shut off and there isnt airflow anyhow , whic will send dye in all directions as it wont be influence by the airflow across the evaporator. Hope this helps.
I split this thread so it may get more responses. Good luck.
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Old 06-01-2012, 08:08 PM
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Thanks.

The threads are clean right now. What happens if there is some ester oil left in the system and you recharge it with refiridgerant infused in a Pag oil r134a refridgerant mix?

Are ester and Pag oils compatible?
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Old 06-02-2012, 12:14 PM
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If you use a synthetic PAG , it's compatible with all 134 oils.Cool Blue is good stuff.
I would recommend flushing the system well, to remove as much old oil and debris(if any) and replacing the dryer.
No way to flush the compressor. Be sure to clean the orifice tube(inside the liquid line) .
Dont get too much oil in the system. After flushing very well, put about 3 ounces in the evap core, (one for evap,one for condenser, and one for dryer). Then, connect the line, evacuate and recharge.
When charging, dump the first can of freon in the low side a little slow, to help get the oil moving, so as not to dump too much at once into the compressor. After the first can,charge as usual.
BTW Be sure to use an approved flush solvent. Bright solutions makes one. Just shop around a little before going to Mc Parts. Dont let them sell you some thing besides what you know to be correct.
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Old 06-02-2012, 12:20 PM
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This stuff is about 18 bucks at grainger. Looks like it would work well.
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Old 06-02-2012, 03:54 PM
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Missing information

You didn't say whether the system is or is not cooling...or if there really is a problem other than the hiss you hear. The hiss should be from the expansion device, not the compressor. If the compressor hisses, you've got at least one busted suction valve, as they are the first to go if you've slugged it with liquid refrigerant (very cold, metal flapper valves don't like it VERY cold, 'cause the metal get brittle and breaks off. But you still may have lost a discharge valve too. Generally, if you loose an intake valve, it will trash the compressor, so if it's still running, it would more likely be the discharge valve.

If you have put two cans in, and it's still not cooling, and you've lost your valves or one or two of them, the pressures will not be "correct". The suction will be too high, and the discharge will be low.

Tell us what your pressures (suction AND discharge) are at 1,500 rpm, outside temperature, temperature at one of the grilles, fan on high, pulling in outside air (NOT recirculated air).

If you REALLY have a leak, you need to borrow or buy a halogen leak detector. That's the only way you will find a slow leak. But if you are basing your belief that you have a leak from a "hiss", you probably don't even have a leak.

(owned an HVAC company for 30 years)....
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Old 06-02-2012, 04:48 PM
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Quote:
Originally Posted by '49 Ford Coupe
You didn't say whether the system is or is not cooling...or if there really is a problem other than the hiss you hear. The hiss should be from the expansion device, not the compressor. If the compressor hisses, you've got at least one busted suction valve, as they are the first to go if you've slugged it with liquid refrigerant (very cold, metal flapper valves don't like it VERY cold, 'cause the metal get brittle and breaks off. But you still may have lost a discharge valve too. Generally, if you loose an intake valve, it will trash the compressor, so if it's still running, it would more likely be the discharge valve.

If you have put two cans in, and it's still not cooling, and you've lost your valves or one or two of them, the pressures will not be "correct". The suction will be too high, and the discharge will be low.

Tell us what your pressures (suction AND discharge) are at 1,500 rpm, outside temperature, temperature at one of the grilles, fan on high, pulling in outside air (NOT recirculated air).

If you REALLY have a leak, you need to borrow or buy a halogen leak detector. That's the only way you will find a slow leak. But if you are basing your belief that you have a leak from a "hiss", you probably don't even have a leak.

(owned an HVAC company for 30 years)....
If the reed plate or "valves" has an issue with the reeds sealing, you will have a nasty fluctuation in the low gauge and a similar fluctuation in the high side. Usually a reed will be damaged when a "hydrolock" or liquid enters and the compressor cant compress it (naturally) damaging the reed.A damaged reed or valve on the high side only, would create a fluctuation on the high side only.
Pressure equalization usually is the expansion device or in this case an Orifice tube, as it is a CCOT system, not a TEXV.
Flourescent dye , a black light , yellow glasses and a real dark shop is the best way to track a leak. It also works good for a customer as they like to "see" things for themselves.
Oil residue with dye will be present at any leak.Those electronic leak detectors are so flaky, just bumping them sets them off.
A gauge reading as 49 ford coupe said would be helpful, please. I wa sassuming you had a charge in it at the time of your post.
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Old 06-02-2012, 07:45 PM
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Guess ol' Spinn got it fixed.

Ya think ?
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Old 06-03-2012, 07:42 AM
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Originally Posted by '49 Ford Coupe
Ya think ?
Lets hope so. Its fixin to get hot out there.
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Old 06-03-2012, 10:24 AM
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Yes it is blowing snow balls. Time will tell for how long.

Thanks all, the system is a salvaged one, and it is old. It was brought into a vacuum and held it. There are a few mysterious hisses, but they could be normal. Compressor cycles well. I think its ready for the heat.

The ole gauges read, 24 low and 240 high. However the needleds in them are pretty floaty.

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Old 06-03-2012, 12:29 PM
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High side is a bit high. Try to seal the area between the radiator and the condenser with some foam and glue it down with weathersrip adhesive.
Anything you can do to promote absolute airflow acrros the condenser at all speeds, especially when at a stop, will help the duct temp, and lower the high side pressure. Helping the compressor to live longer by keeping high side pressure down is a plus.
Also check to be sure the recirculate door will close( AC MAX I think) as it recirculates the allready partly cool and de humidified air inside the cab. It will make it much cooler and help to lower high side pressures as well.
Glad to hear it works either way.
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Old 06-03-2012, 02:08 PM
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Coming back from church I noticed that after it has been running for a while , the compressor starts to vibrate a little. The temperature stays cold and the the cycling is unaffected. No bearing noises, or belt missalignment. Only happens running in the heat of the day so far.

Could this be from high pressure?
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Old 06-03-2012, 02:19 PM
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Quote:
Originally Posted by spinn
Yes it is blowing snow balls. Time will tell for how long.

Thanks all, the system is a salvaged one, and it is old. It was brought into a vacuum and held it. There are a few mysterious hisses, but they could be normal. Compressor cycles well. I think its ready for the heat.

The ole gauges read, 24 low and 240 high. However the needleds in them are pretty floaty.
I have had much better luck finding small leaks with pressure rather than vacuum. We have an old A/C hose that we adapted a air hose fitting onto. Put 150LBS of shop air into it and see if it holds. This and some soapy water somethin will find the leaks that other methods failed at. We also have a black light yellow glasses kit and that is our first line of testing.
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Old 06-04-2012, 12:05 PM
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Hey, LATECH

"Those electronic leak detectors are so flaky, just bumping them sets them off."

Beg to differ with ya....Yes, they are highly sensitive, and you have to purge them when you get into a "big leak" and it overpowers the sensor, but you just wave it around in the air away from the leak for 10 seconds and they usually clear up. (If ya don't know how to use it, yea, it can be a pain in the ***). Maybe some cheap ones that have no sensitivity adjustment might set off by bumping (NEVER seen that in the dozens I've been exposed to), but any ordinary leak detector will find leaks that have NO oil residue (mostly on suction side), and can detect leaks that may only be less than an ounce a year. I've always used an electronic leak detector, and have found hundreds of leaks that were otherwise "unfindable" if that's a word...

Evaporator leak? stick the probe up the drain line or in to supply outlet after it has sat a while without running. How ya gonna do that with soap bubbles? Caint.

And how about tiny leaks when you can't see the bubbles or dye? You will MISS the leak.
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Old 06-05-2012, 10:45 PM
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Quote:
Originally Posted by '49 Ford Coupe
You didn't say whether the system is or is not cooling...or if there really is a problem other than the hiss you hear. The hiss should be from the expansion device, not the compressor. If the compressor hisses, you've got at least one busted suction valve, as they are the first to go if you've slugged it with liquid refrigerant (very cold, metal flapper valves don't like it VERY cold, 'cause the metal get brittle and breaks off. But you still may have lost a discharge valve too. Generally, if you loose an intake valve, it will trash the compressor, so if it's still running, it would more likely be the discharge valve.

If you have put two cans in, and it's still not cooling, and you've lost your valves or one or two of them, the pressures will not be "correct". The suction will be too high, and the discharge will be low.

Tell us what your pressures (suction AND discharge) are at 1,500 rpm, outside temperature, temperature at one of the grilles, fan on high, pulling in outside air (NOT recirculated air).

If you REALLY have a leak, you need to borrow or buy a halogen leak detector. That's the only way you will find a slow leak. But if you are basing your belief that you have a leak from a "hiss", you probably don't even have a leak.

(owned an HVAC company for 30 years)....
The compressor has continued to hiss on shut down, vibrate on hot days , and the high side number fluctuates. That is beginning to sound like the discharge valve. However the system blows cold air and still shows no leaks. Thermometer pole says 50 deg. The high side seems high, but was told a r12 convert to 134a will be higher. The vibration I thought to be noncondensables , oil in the compressor, or a mild overcharge. Now with the hiss, your post has me thinking.

Somethings not right, it works but not how I want it to. Are compressors rebuildable? Are you guys EPA 609 certified? You should be , good stuff.
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