Automotive Air Conditioning Information Forum

I recently installed a new complete Ac system in my 2000 dodge ram 1500 5.2 V8 (new compressor, evaporator, condenser, accumulator, lines, orifice tube, etc). Also keep in mind that I live in Florida so the weather is hot. I put in the correct amount of oil and exact amount of refrigerant (32oz) that the truck called for using an Ac service machine. The ac blows cold and works good at idle but it cycles on and off every 3-5 seconds going down the road. The system is of course aftermarket. With Ac off both high and low sides show equal pressure at 75psi. When Ac is on full blast at idle, the low side shows 30psi and high side is 120psi. When I Rev up the engine, the low side drops to 20psi and the high side goes up to 150 psi and the ac clutch cycles off. Is it acting like it's still low in refrigerant? What should I do?

You are low on refrigerant. And please post ambients when posting pressures and vent temps.
With RPM at 1500, I would slowly add refrigerant (very slowly) until the low is 30 psi. You may have to go to 35 psi. Keep track of high side pressures and vent temps as you do this, and report back. Weigh it in if possible so that you know the final charge.
Chances are good that it does not need much more.
If you have a service machine this should be easy to do.

Thank you for the reply. Temps right now are 85 degrees with lots of humidity. Is this common to need more than the specified refrigerant amount?

Since system is aftermarket, all bets are off. There can be slight manufacturing differences. You do what you have to do.

I hear you. If the temps down here are 85 to 90 degrees right now, where should my low side psi/ high side psi ideally be at idle with ac on full blast?

we don't worry about idle pressures, they have no meaning. compressor does almost no work at idle.
shoot for the low as mentioned at speed and then report back what you get for a high, including vent temp

OK. I will do that. Thank you!

I, too, think the system is somewhat low on refrigerant.

Presuming that you're testing under the proper conditions, not at idle, a low-side pressure of 30 PSI correlates to an evaporator temperature of around 34°F, which is just about right. We'll wait for you to post the high-side, center vent, and ambient temperature readings as suggested.

I'm not a professional, but I also believe you are low on refrigerant:

Moorenycc wrote: ↑Thu Sep 21, 2023 6:48 am When I Rev up the engine, the low side drops to 20psi and the high side goes up to 150 psi and the ac clutch cycles off.

I'm in Arizona, so not as cool as Florida. At about 2000 rpm, I would expect low side pressure to be about 30-40 psi and the high side pressure to be about 250 psi.

UPDATE: I added about 4 more ounces to my system. The system is working better and the compressor is sounding better. Believe it or not, I still couldn't get the low side up to 30 psi at 1500 rpm, it only got to about 26psi. At idle on full blast, the low side is sitting at 35psi and high side is 160 psi. Tempurature outside is 86 degrees and 54% humidity. The center vents got down to a tempurature of 45 degrees. It's cycling on and off less frequently but it's not working perfectly yet. Should I keep going with more refrigerant or am I going to far?