AC compressor clatters on startup


Old 08-21-00, 11:47 AM
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My 18 year old Carrier VJ series (2 ton) unit
had two lbs of R22 added recently. There
were no problems, and it was cooling fine.
Now, when the compressor starts, there is
a very metallic clattering noise coming from
the compressor. Its not the fan, and the
fan motor and blade spin freely and are not
touching the housing. The tech I spoke to
says that the two lbs added put a strain on
the compresssor at startup, as the noise goes
away after its 'up to speed'. He offered to
bleed off some of the freon, and says that
the reduced strain on the compressor will
alleviate the noise, and prolong the life of
the compressor. I've never had any trouble
with the unit and I was wondering if anyone
has any experince with this 'reduced charge'
fix. There was no noise before the charge,
and it was cooling fine. The charge was
added at a routine checkup, after going 10
years since the last checkup. -- Thanks
Old 08-21-00, 03:52 PM
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Hi Minnesoda:

When I read posts like yours, I get UPSET. The only reason to add refrigerant is if there is a leak. The leak should be fixed first, then dehydrate and recharge the system. Two pounds in a 2 ton system that was probably fully charged is a lot of overcharge. It is illegal to bleed refrigerant to the atmosphere. May I suggest that you have someone else look at it and get the charge where it belongs. The clattering you're hearing may be the compressor pumping liquid refrigerant which would wipe it out in short order. There is no reduced charge fix; there is the correct charge which is acheived by following the manufacturers directions. Adding and bleeding off is by guess and by golly. Thanks. John.
Old 08-21-00, 08:07 PM
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John is right on the money!
It really fires me up to come in behind someone that has not done a complete SYSTEM check. I've seen a lot of techs that are to quick to adjust a charge without having checked out the entire system first. Systems are sealed, and any abnormal pressures mean one of two things. Either the refrigerant is leaking or something else has caused the pressures to deviate from the norm. When you get so-called techs that start adding, adding, get the right pressures...the next thing you know you have a compressor lockup.........Your's sounds like it's on the edge. Anyone can put a set of gauges on a system and adjust for so-called normal pressures. That does not mean the system is charged to the correct level. Check all filters, ducts and coils first.
Old 08-22-00, 10:23 AM
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Thanks for your prompt replies.. I don't
think its a serious leak. The connections
are compression, not soldered, and I'm under the impression that a 'little' loss is normal. About 10 years ago I had it checked,
and the tech said it was one lb low. I had
it checked again (a couple weeks ago) because I'm aware of the dangers of too low a level. The tech checked the plate, read the gauges, said I was 2 lbs low, and stuffed it in.
There is nothing else wrong with the nit. I keep it clean, the filters, clean, and it was cooling just fine. Sounds like I need a second opinion. Thanks!
Old 08-22-00, 02:53 PM
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Hi Minnesoda:

Carrier has a procedure for fixing leaks at the compression fittings. It involves sliding the nut back on the tubing and soldering the ferrule to the connector. I don't like their method and I usually cut the leaking connector out and braze in a section of new tubing with an access valve and sometimes a shutoff valve. If you haven't needed refrigerant for 10 years, I doubt you have a leak. My bet says the guy saw a suction pressure lower than normal and just shoved gas in without checking the superheat. An 18 year old system is bound to have a dirty cooling coil even if you've been religous about filter changes. Second opinion sounds like the way to go but tell the tech the whole story. Thanks. John.
Old 08-23-00, 06:32 AM
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Thanks BigJohn.. The second opinion I got
yesterday, is that even if it was overcharged, the increased pressure would not
be a problem unless the unit was short-cycling. Apparently there's an
equalizer 'valve' that equalizes the pressure
across the 'piston' such that after 5 minutes
or so, there is not much pressure to resist
at the start. I'm sorta inclined to believe
that since the clatter dosen't occur on EVERY
start, just seems to happen when the unit
is on/off during hot spells. I'll pay more
attention to the lapsed time between starts,
and try to correlate the time span and the
noise. The second opinion was just to let it
go as-is, i.e. a 'pump-out' to reduce the
R22 wouldn't help much. He said just to let
it go, until the noise becomes constant, then
likely swap-out the condensor. I will,
however, clean the fins on the A-coil.
Thanks for all your help.

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