wont hold vacum but will hold pressure

[supercarpt722]

Good morning .Working on a john deere 9510 combine.Customer says he has repaired it just wants us to charge it.Ok I go and oull a vacum on system.Find it has r134 in it and is over filled.Recovered 6.57 pounds when book says should only be 4-4.5pounds.Get done with recovery and tried pulling a vacum.Looses vacum in under 5 seconds.Also can only get to about 12 of vacum.Im kinda new at this.Any help would be much appreciated.

[Cusser]

The leak could be in your AC system or in your equipment; check out the equipment first for leakage.

[Tim]

How do you know it is holding pressure?

[Cusser]

How do you know it is holding pressure?

My interpretation is that since there was R134a in the system (6.57 pounds ) that he ASSUMES that it's holding pressure. I would think a big leak would even be able to be heard and would not hold 6.57 pounds for long. So I suggested for him to do a vacuum test on just his equipment.

[Tim]

How do you know it is holding pressure?

My interpretation is that since there was R134a in the system (6.57 pounds ) that he ASSUMES that it's holding pressure. I would think a big leak would even be able to be heard and would not hold 6.57 pounds for long. So I suggested for him to do a vacuum test on just his equipment.

I don't disagree with you. I just never saw any indication of a leak test at all.

[supercarpt722]

machine sat outside for about a week and inside while i changed the front main seal on engine for a few days also.Unfortantley customer tried to repair himself.I was handed this to only orginally to just charge system after he repaired it. No idea what he repaired or how much r134 he put in it to start off .So it held 6 pounds for sure over a week and a half.I will go and double recheck my equipment tomorrow morning.As for a leak test please do expain more.Low side gauge was at 70 high side around 45 if this helps.Also my understand is it has pressure in sytem if there 6 pounds in it.Correct?Like i said in first post im new to this a/c stuff. Learning as i go. thank you

[ice-n-tropics]

Compressor shaft lip seal has 2 lips. one for positive pressure and one for negative (below ambient pressure). If front shaft seal is nicked by sharp shaft step during installation, then it my leak vacuum. Debris or overheating due to clutch slip or undercharge can also cause shaft seal to leak vacuum.
Hope this helps
hotrodac

[swampy 6x6]

hi

First look for obvious damage eg hose rub thru . Twist hose ferrules if they twist replace
Look for oil stains on all a/c parts
Has the system have leak dye

might see compressor seal vacuum fluctuation reading on a micron gauge when clutch is rotated .
or
charge with a trace of refrigerant and top up with nitrogen to 250psi . Then electronic leak detect and then use bubbles

Compressors donot like seal replacements unless very young . If a compressor is even only middle aged change it out . As I said earlier a micron gauge can see a small seal leak . If i was confident the seal was an issue I would rather have a working AC than 10hrs inside a machine without it .



NB worn out manifold/hose sets can leak really bad to give your unusable situation
Take the gauge set of machine and vacuum test with lines plugged . Does it obtain 29 in vac and how long can it hold ?

The R134a service fitting o ring cannot be tested unless a dummy fitting is installed
The manual version leak on threads and manual turn knob nut/shaft [may be covered by sticker ] Use nylog to stop these
The manual turn knob shaft seal leak some times the air flow be felt or heard
Most R134a connectors are barely avg quality