Automotive Air Conditioning Information Forum

I have a 99 F250 7.3 Powerstroke that had a leak in the discharge hose. I replaced the hose, vac'ed the system and then charged it.

The ambient temp was 80 when these pressures were taken.

The compressor is not cycling off so I think this means the low side should be under suction. If this is the case, the low side pressure is probably too high.

The high side sits around 100psi when the AC is off but when turn on it builds to 175 and remains there.

I charged the system with a 30lb tank so i relied on the pressure to know when it was full. The system take over 2lbs of r134a but the tank feels a good bit lighter and I think it may have been overcharged.

The AC is working great but I've noticed a weird noise under the hood when I first start the engine which is another reason I am concerned.

I'm wondering if this behavior could be caused by a failing compressor that isn't building the correct pressures or a blocked orifice tube.

I'm just a shade tree mechanic so any help from the more experienced would be greatly appreciated.

Rkulp89 wrote:I charged the system with a 30lb tank so i relied on the pressure to know when it was full. The system take over 2lbs of r134a but the tank feels a good bit lighter and I think it may have been overcharged.

Most experts on this site only recommend to charge by weight.

If the system worked fine before the hose rupture, then I'd guess it would work fine with correct amount of refrigerant if just a discharge hose was replaced.

Just to clarify, the system is working and blowing cold (around 50F).

It could have been running like this before the leak and I would have never know. The noise is the only thing new I've noticed and I'm still tracking down where exactly it is coming from because it is only auidble for the first couple seconds after I start the engine.

The behavior of the pressure gauges is what I am hoping I might get some answers on. I thought they should be fluctuating while the compressor cycles, but neither are happening.

Open both doors on the cab.

Set the cabin fan to the highest speed.

With your gauges attached, raise the engine rpm above 1500 rpm. Observe & record the pressures while at the elevated rpm, and post them here.

Depending on the ambient temperature when those readings were taken, things look pretty good.

Cycling will happen when the low side drops far enough. If the evaporator is not icing up, the low side pressure is fine.

If it will not cycle when the low side drops below 22 psi, then either your cycling switch or gauges are suspect.

Between zero adjustment, and allowable gauge error you can be off by 5 psi.

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