Should a/c compressor cycle on/off while driving?

[wheelsup]

JDS,

Yes I know the rise was not due to a leak. That is what I was getting at. If it was a leak it would rise every time I pulled the vacuum.

I regulated the pressure to 120-130 output. My input pressure would bleed from 150 down to 120-130 and I would close the service port. Then shut off the air supply. Let compressor build up pressure and then repeat the process. I had a very steady 29" indicated on my gauge, it held for 15-20 mins or so.

Are we focusing on the wrong thing here? I am more concerned about the repeatedly cycling of the compressor.

[wheelsup]

Also wanted to say I understand why you would want me to cycle the compressor. It would equalize the pressure. Makes sense. Don't mean to be argumentative. However when I was gas 'n go with air all in the system prior to this the output temp was less (30's) and compressor did not cycle unless it was low on refrigerant.

[JDS60R]

not cycling is a sign of bad efficiency. If it can't reach its target cooling temp it stays on. You want cycling or need to find out why it isn't. At 100 degrees almost none of them are cycling.

Your old gas n go system with no cycling was less efficient, cost you more in gas and would have a very high "high side" pressure to get you under 40 degrees. Knowing that system I would second guess your temp measurement equipment, as getting to 39 degrees output air with a 80 degree input (with air in system)is very difficult without critically high head pressures. With the high head pressures you also get a swing in efficiency on stationary vs moving. A properly drawn and filled system is much more consistent and efficient that the gas and go system. These are laws of physics - not my impressions.

I do believe you are seeing hotter temps now due to all the air in the system. I think you will be pleased when its drawn correctly and charged fully. It will cycle and be consistently colder than before.

[wheelsup]

Do you feel that 6-9 sec cycle at higher RPM (above idle, 2300 +/-) is normal though?

I'm get the 134a recovered and suck it down again. Turning the compressor over. Or maybe just have it done somewhere.

[JDS60R]

Matt,
Do it yourself with the process we talked about. You could buy a nice vac pump from HF for what they would charge you. Your cycle time at rpm depends on a few things including head pressure, ambient temps, output temps, compressor efficiency and system blockages (assuming no unnecessary ones.)

I am betting you are hitting your high side limit and that is why its cycling off ( I guess this as if your ac vent temp was pleasing you would not be addressing this as an issue)

Once pulled down I think you will see longer cycle times especially as ambient rises in the summer.

[wheelsup]

Yes the vent temp is decent. Not cold but certainly very cool and livable on an 18 year old compressor. I'll give it a go, hopefully it reduces the cycle time, that is mostly what I am concerned about, wear and tear on clutch plus slightly annoying on/off tug on the car.

[abscate]

I got the pump and AC manifold on the proverbial sale plus a one time 40% off and was about 80 USD all in....SCORE!!

[wheelsup]

So I realized something. 1.63# is 26oz of 134a. I only put in 22 or so, so it's around 15% undercharged right now. Going to add the rest of the can I have left to see if it helps in the cycling.

[wheelsup]

OK doing some more reading. No need to pull another vacuum on the system. Each side is connected via the orifice tube.



That small copper tube connects both sides of the system. When a system with an orifice tube design is shut off both sides equalize in pressure. This is also why a system with an orifice tube has an accumulator - to serve as a place for refrigerant to pool and expand to the vapor state before sending it to the compressor.

In a system with an expansion valve (not ours), a receiver is used. It is placed after the compressor and before the expansion valve. The receiver contains liquid refrigerant and serves as a means to supply the expansion valve with liquid refrigerant continuously. No accumulator is used because the expansion valve closes off the high and low side of the system preventing liquid refrigerant from migrating from the high to low pressure side.

I'm going to add more refrigerant to fully charge the system and see where that gets me.

[abscate]

You need to pull down both sides with vacuum pump. Are using a dual gauge AC adapter or trying to adapt a vacuum pump with fittings?

On edit..incorrect as noted by Matt below. System design has single port and no HP port