Noisey engagement

[forestg]

I have an R12 system that has been opened several times over the last 28 years with never a problem. This spring it was low on gas and I discovered a leak around the plug in the bottom of the block style expansion valve. I replaced the expansion valve and installed a new drive belt. After this the clutch makes a horrible grinding sound when it engages but the compressor runs smooth and quiet. Since the only change was the expansion valve I purchased another one of a different brand and installed it with the same results. My wife couldn't stand the noise and told me to replace the compressor as that must be the problem. I could not feel anything wrong with the compressor but installed a new Sanden 508 anyway with no change in results. I don't know if there is liquid getting into the compressor or what is causing this noise. The belt does not seem to slip on engagement. Since the compressor mount slides in four slotted holes to adjust belt tension is it possible that the compressor is slightly cocked so that the belt pulls to the side? Would this cause a noisey engagement? I don't know where to go next. This system has always been so quiet that I connected a pilot light to let me know when it was running.
Thanks for any thoughts.
Forest

[cm5400]

Car make, model and year would be nice...

[forestg]

Well, it is a 1972 Pantera with mostly custom parts. I know everyone always wants pressure so low side is just under 30 and high side about 160 at 70 ambient. The AC works fine and cools well other than the grinding noise as the clutch engages.

[Tom Greenleaf]

Couple ideas: This car should have a sight glass to know charge is right - use it.

I'd also consider reducing clutch air gap to the minumum such that it doesn't rub when disengaged,

T

[forestg]

Like I said, mostly custom stuff. No sight glass but charged with 2 pounds R12 just like every other time and no problem before. This started all at once when the expansion valve was changed and new belt installed. I replaced the expansion valve a second time with no change. This problem must be due to either the valve or the belt install. Can an expansion valve allow liquid to get to the compressor?

[ACProf]

One of the jobs of the expansion valve is to PREVENT liquid from leaving the evaporator. It monitors the exit temperature of the refrigerant and compares that to the incoming temperature (by pressure) and adjust the flow accordingly, so that the exit temperature is 3-5 degrees warmer thusly insuring all the refrigerant in the evaporator has been vaporized.

ACProf

[Tom Greenleaf]

Great that you know the charge that at least has worked before.

As the Prof says you can tell tons by touch and feel or infrared temps devices about what is happening where and can tell you where a problem is lurking.

Knowledge base above has lots of neat info to help and I'd struggle but have a real neat chart that I plain don't know how to post here yet that shows that if you know the temp you would also know what pressure is in that item or area - helps with diagnostics.

Ex: R-12 when it's exactly 100F should be 117.2 PSI! The chart is a curve but well documented.

Another trick that may help is to use "Brakleen" on contact area of clutch. Keep that stuff away from painted anythings or rubber anythings! It evaporates fast but would de-grease or clean the friction area.

If this noise is a belt issue try some WD-40 on the belt. If it quits they are making belts that are dang silent - Gatorback by Goodyear is one. Pully surfaces shine up fast even with the serpentine ones. Pulleys need to be in near perfect alignment as you know also,

T

[Tom Greenleaf]

See if I can get a chart to show?? There are better ones out there that this but gives the idea:




T

[forestg]

It is not a belt issue nor a clutch issue. It seems to be a slug of liquid in the compressor. If it is off for a fair period of time it engages very smoothly and with no noise but when it is cycling there is a definite rumble from inside the compressor. I screwed in the plug in the bottom of the block valve which I believe increases the superheat value and the sound has diminished somewhat but is still there. I have ordered another expansion valve and am considering whether to install an accumulator between the evaporator and the compressor.
Thanks for the insightes provided.
Forest

[Tom Greenleaf]

Maybe chance but never happened to me without an overcharge situation?? Too much oil (it would take a lot too much for this) or the charge is too full IMO if this is in fact the compressor choking on a liquid which should not be available at inlet if all is well and clearly it isn't but I don't know without seeing this in front of me for now,

T

[forestg]

Follow up to my problem. I started over with another new expansion valve and noticed that the suction fitting seemed to not feel right when being tightened. Removed the line and valve and looked closely at the fitting and the valve. The fitting I used was a long pilot o-ring style and the pilot was bottoming out on the stem inside the block valve. I shortened the pilot, installed a new valve and now everything works right.
Thanks for the suggestions from everyone.
Forest