Groaning/Moaning Noise (1998 Chevy C1500)

1998 Chevy C1500 w/5.7L. Replaced the main AC hose (accumulator-compressor-condenser) and the orifice tube. Pulled a vacuum to about 280 microns. Added two cans of R-134A and 3 ounces of oil. Nice cold A/C now, but there is a moaning/groaning noise around 2500 RPM. I goes away around 3500 RPM. I can hear the compressor clutch disengage when the noise goes away. If I jumper the pressure switch the noise will stay there after 3500 RPM. Gauge readings with the car not running are L-87 H-95. With the car running at idle L-31 H-176. Any idea what the noise might be? The noise correlates with the RPM. Faster RPM the noise pace picks up. It isn't real loud but you can hear slightly when driving. Doesn't sound like a mechanical noise. I put a hose to my ear and to the compressor and could not ID the noise coming from the compressor. I am thinking I may have a high pressure issue.

1998 Chevy C1500 w/5.7L. Replaced the main AC hose (accumulator-compressor-condenser) and the orifice tube. Pulled a vacuum to about 280 microns. Added two cans of R-134A and 3 ounces of oil. Nice cold A/C now, but there is a moaning/groaning noise around 2500 RPM. I goes away around 3500 RPM. I can hear the compressor clutch disengage when the noise goes away. If I jumper the pressure switch the noise will stay there after 3500 RPM. Gauge readings with the car not running are L-87 H-95. With the car running at idle L-31 H-176. Any idea what the noise might be? The noise correlates with the RPM. Faster RPM the noise pace picks up. It isn't real loud but you can hear slightly when driving. Doesn't sound like a mechanical noise. I put a hose to my ear and to the compressor and could not ID the noise coming from the compressor. I am thinking I may have a high pressure issue.
With out hearing and testing we can have no idea of noise.
But some proper testing and correct amount of R-134a and correct adding oil may get to your problem/noise.

System takes 32 % R-134a
Just 2 - 12% cans leaves your system 6 % or more low.
But pressure would be low if R-134a is low.

If you suspect pressure problem you need to get pressure readings with low and high side gauge set at idle and at 2K RPM.
And watch for pressure or gauge needle fluncating when noise is going on.
To much oil or not emough could make noise.
Also watch belt for deflectings or flooping.

I would suggest the correct amount of R-134a and pag oil and gauge readings to start with.
Post back your pressure readings.
Some compresser comewith 6-8-10 % of oil in them and or some are dry.
When installing a compresser it should have oil drained out of new compresser before installing and the add 2 % pag oil for compresser and 2 % oil for it .
And 2 % for reciever dryer and 2 % oil for a dry condenser.

Was it a rebuilt or new or used compresser?
Did you drain compresser and check amount of oil in it before installing it?

If you have to much oil in system you will need to flush system and then add correct amount and kind of oil

when replacing the compressor you drain out the oil. then you add new oil . making sure you add the correct amount. not sure how much your vehicle takes exactly but, adding 2more OZ than what is stated/required is safe. not having enough will cause the compressor to make rattle noises at all speeds.PAG 150 oil is used .

It is quite possible this is the compressor pulley bearing making the noise or the compressor bearing... If the compressor bearing is the cause you will start to loose refrigerent...

the pressures you post must include air temp of the area . fan on max , doors open, engine at 2000RPM.

I would expect at 80deg f to see about 200psi on the high side. about 40psi on the low ...175psi sounds good at 70 deg f

check the belt for proper tension..

many have had problems with these compressors purchased lately.

Appreciate the replies. I will take the 2K RPM readings today. I only replaced the hose and the orifice tube. Not the compressor. When I first noticed the noise I suspected possibly being low on oil so I added the 3 ounces. No change. I also should mention the AC has not worked in this truck for a couple years. Should the pressures readings change at the 2K RPM?

Current gauge readings at 86 degree ambient temp not running (L 115 H 120), at idle (L 32 H 200) and at 2K RPM the compressor cycles off at (L 60 H 218) and then cycles back on gain when the pressure drops. Suspecting I may have a restriction. I replaced the orifice tube, that is about all I can think of.

Current gauge readings at 86 degree ambient temp not running (L 115 H 120), at idle (L 32 H 200) and at 2K RPM the compressor cycles off at (L 60 H 218) and then cycles back on gain when the pressure drops. Suspecting I may have a restriction. I replaced the orifice tube, that is about all I can think of.
What is low and high at 2K rpm with compressor running or jumped?

You are More like low on R-134a.
As in first post 2 cans will not fill system.

Add some more.

Restrition would build up high pressure on high side and drop low side pressure.

Does the noise come in more at any certain pressure or just any rpm?

MT,
Thanks for the advice. I will add another can. How many cans should it take? The noise isn't there at idle but starts around 2K RPM. At idle no noise. The compressor cycles off once the pressure is around (L 60 H 218).

Did you not read post no. 2 ?

I didn't understand the percentages. After reading post 2 again I think I got it. 1 more can would be the 6% more I need. Sometimes I am a little slow :). Thanks for pointing me in the right direction.

I didn't understand the percentages. After reading post 2 again I think I got it. 1 more can would be the 6% more I need. Sometimes I am a little slow :). Thanks for pointing me in the right direction.

Each can is 12 oz.
2 cans is 24 oz.
1 more can is 12 oz more that would overchage your system.

Your system calls for 32 oz. R-134a.

If you have 2 full cans in it.
Just add 8 more oz.
Like 12 oz and 12 oz and 8 oz makes 32 oz.
Set the can on a weighing scale that will read oz. and you are set to go.
Just do not let the cops see you weighing the R-134a or they may start asking questions.:lol::grinno::rofl:

Appreciate the replies. I will take the 2K RPM readings today. I only replaced the hose and the orifice tube. Not the compressor. When I first noticed the noise I suspected possibly being low on oil so I added the 3 ounces. No change. I also should mention the AC has not worked in this truck for a couple years. Should the pressures readings change at the 2K RPM?

since the ac has not been working for sometime this may be the compressor valves,making the noise could be its going to fail.

you do need alittle more refrigerent. the noise is not from being a little low on that..

two things effect pressures air temp of the operating environment and amount of charge , engine RPM with ac blower at max..

2 ,ooo RPM is what is used along with the air temp at time of pressure testing..with this I can say if the system is working and charged correctly.