I have a 2000 nissan maxima 6cyl. It was not cooling all that well, so I added a can of freon and purged a little air out afterwords. It now cools excellent, but now it seems to have a slight wizzing sound to the compressor. Could you tell me what you think this is.

First off, you can't purge air out of a system that has refrigerant in it. You just vented some refrigerant.

The noise your hearing is the compressor knocking now. It could be overcharged, underlubricated, running too much pressure or just getting ready to lock up.




78 Corvette Pace Car For Sale-18k mi orig-Florida

milling; You can't 'just add' freon. It is a very precise measurement. Too much or too little can cause compressor damage.
Loren
SW WA

I let some freon out, but it still has that noise. I will have to evacuate the system and put the correct amount in. Could it possible be the clutch?

No, it's likely a failing compressor for some reason. See if it's still noisy with the exact charge.




78 Corvette Pace Car For Sale-18k mi orig-Florida

I have to agree, it sure sounds like it could be a comp problem and you really have to make sure you have the correct charge to make that call, also make sure the belt is in good shape & the condensor is clean....... Some pressure readings, vent temps & ambient temp would be very helpful


(This post was edited by Sidom on Sep 1, 2009, 3:45 PM)

Thanks for responces, I will put the correct charge in tomorrow and post the results. The reason I purged it was because and old service manual I have says a 1 second purge is equivalent to pulling a vacuum with a good vacuum pump for a half of and hour ( I took some air conditioning classes years ago).

Quote

That's just total nonsense. The only thing you accomplished is to vent some refrigerant into the atmosphere. Using a vacuum pump is done to boil moisture away. You certainly didn't do that.




78 Corvette Pace Car For Sale-18k mi orig-Florida

In Reply To

Thats a new one to me.... Personally I believe nothing beats pulling a deep vacuum.

Now don't take this wrong, because I'm knocking you but if you remember the theory behind this I would be interested in hearing just for the fact I haven't heard it before. It won't change my routine but I still would like to hear it.....

I will try to find the manual, and post exactly what it says it was a refrigeration service manual. I will post it tomorrow if I can find it.

The service manual is maytag side-by-side refrigerator service manual. It has an alternative method for repairing sealed systems. It says ---- Sealed system sweep charge processing is a modified procedure different from the evacuation method employing a vacuum pump and micron gauge that were used in the past. Through extensive evaluation, we have concluded if the sweep charge procedure is properly done there should be no long term adverse affects on the product performace. Keep in mind that the process of flushing clean refrigerant through the system is equivalent to 20 or 25 minutes of pulling a vacuum with a vacuum pump of lower capacity than those specified. Basically, what they do is charge in about 3 or 4 ounces of freon then purge it out, they do this about 2 or 3 times or something close too this, I did not read the complete procedure.

OK, first appliance refrigeration is going to be totally different but what that is saying is that they are using refrigerant as a flushing chemical to clean out the system. The air would still need to be drawn out after but the flush would probably take care of any moisture in the system that would usually be boiled away using vacuum. They refer to is as a "sweep charge", not merely venting.




78 Corvette Pace Car For Sale-18k mi orig-Florida




(This post was edited by Hammer Time on Sep 2, 2009, 6:45 AM)

Yes, but the air collects at the top of the airconditioning system. This is were the shraeder valves are, it should get most of the air out by purging.

No, that is not true. You can't simply "purge" air from a motor vehicle.

That theory will work in a container of liquid refrigerant but there is not "top" in a motor vehicle. Besides, the big reason for vacuuming is to boil out the moisture. The air is gone in the first 5 minutes of vacuum, the rest is boiling the water out.




78 Corvette Pace Car For Sale-18k mi orig-Florida

I should butt out as it's already said. Air is not hiding at the top and many MVAC (Motor Vehicle Air Conditioning) systems have ports at the lowest areas so there goes that theory!

HVAC and MVAC share some principles but not all. You home has a constant RPM for example - you car doesn't!

I'm not claiming to be HVAC certified but getting moisture out is primal to A/C anything and simple venting can't do that. Worse - oils used in lubricating compressors are hygroscopic and turn acidic with moisture in motor vehicles. Total destruction if not payed attention to! I believe all PAG oils are hygroscopic and can self destruct.

Lots of things are different - gasses used, compressor styles etc. Cars since model year 1994 are all 134a - homes, refrigerators etc could be all other gasses depending on maker. An ammonia gas was or is one used for home or commercial/use!

T

PS: R-12 was discontinued new by the Montreal Accord and some 40 countries agreed not to make it new after about 1993
_________________________________________

Tom Greenleaf - MetroWest, Boston

Just another additional point to make here.

I don't know when that article was printed but I can tell you that method would be against federal law now, whether on an appliance or a car. You cannot purposely vent refrigerant now.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Thx 4 the info

As HT stated that is an appliance a/c system plus it looks like they are flushing & then recharging. That would probably remove most of the moisture but not the air on an automotive system. Not to mention is now illegal.

I will tell you that procedure sound real similar to purging air out a freon tank in a recycler. Both systems have storage tanks and air goes to the top of both systems where you can purge the air off the top. An automotive system is different, the closest thing is has to a storage tank in the accumulator/reciever drier but there is no way to purge off the top.........