Truck A/C pressure question.

Did you have the system set to MAX AC? High-side pressure is a function of the heat being absorbed by the evaporator, if you are recirculating cabin air then the high-side pressure will show lower than what the chart suggests. Also, every make/model has their own pressure specs. Under 40 psi on the low-side in these temps would have me looking for a leak with a UV light though.

quote:

---

and a fan blowing on the front

---

That's another variable for high-side pressure. I run dual Derale electric fans on my F150 and one is setup to run at max speed anytime the AC is on. The high-side pressure really drops if both fans come on though.

Found this F150 info for you. Thread says it needs 1.5lbs of refrigerant, and these pressures. Not sure if they have the same amount of freon or not. Going off of this, I'd do 50-55, and hope for 275 on the high side. It should be the same for every vehicle, but different quantities.

I'm going to take it that you don't have the equipment to recover-vacuum-and charge the system. Here's what I would do. I make certain windows are up ( absolutely not down)-system on Max and run at approximately 1600 rpms. Feel the smaller line going into the evaporator then feel larger line coming out. If it's cold going in but not as cold coming out the you are indeed low on freon. Low side at 2000 rpm is not far off. A system that is 45-55 ( on a single evaporator system) at idle and drops down to 25-35 on elevated rpm is indicative of a weak compressor. The telltale on this is the system cools better while driving then it does at idle. A dual evap system will typically have low side readings of 40-50 at idle. High side readings can vary greatly depending on many factors. One rule of thumb is twice the temp of the day plus 15%. This is ballpark-not exact. Your hi side readings are close enough to not raise concern. Your chart is "legit" but not religion. Don't get stuck trying to fit exactly into the charts. I think your system is just a little low on refrigerant. If you do have the equipment to recover-vacuum-and charge to correct spec I would do that first so you start with knowing charge is correct. Good luck with it.

quote:

---

recover-vacuum-and charge

---

I have a guy that'll do it for free for me. All he does is hook it up to a machine that is on wheels, so I don't suspect it would be expensive

Thanks for this post.

That's what I was looking for. A blanket chart isn't a one for all as we know. On the right track diagnostic wise beside just pressure and gauges is what I was looking for. More troubleshooting techniques. If this does not work and there is still concern I will bring it somewhere. I prefer the idea of being able to accurately add the amount of coolant by weight.

I cant reclaim but I do have access to a vacuum pump and gauges. As well as a small scale I can weigh I just do not want to just vent all the refrigerant out. I'm not a tree hugger but I don't want to dump all that shite into the atmosphere for zero reason.

Thanks

A leak may very well not show up so soon. I charge and dye many systems and tell them to come back in a couple of weeks or when it stops performing well. A substantial leak will show quickly and if you had a substantial leak you would have been out of freon or close to it instead of just a bit low.

You're most welcome.