Late 99 7.3 F250. Didn't have working AC when I bought it, just blew hot and I didn't really care because I was driving my first 7.3, nothing more exciting than that. Charged it up a little with smaller 134 can and crappy low side gauge last year and it worked for maybe a week. Trying to get on top of it this year and do it right since I'll be towing the boat and 6 month old along with me, changes things a bit.

A/C Manifold Gauges read 20 PSI low side 75 PSI high side (while compressor is running, after adding another small can to get compressor to cycle for testing). Didn't think to do static readings, but I've heard they're fairly useless anyhow. Ambient temp was only 65F while testing though. Compressor runs but is short cycling. About 3 seconds on and maybe 8-10 off. Air gap on compressor clutch is within spec. High side pressure doesn't seem to suggest to me that I have too much air in the system, but I do have a vacuum available if need be.

I was going to add some UV dye but I read somewhere on here that cars built after like 92 had the UV dye added from factory. Only dye I can find with the UV light and yellow glasses was a small run at the pressure switch next to the compressor. I removed the blower and looked over at the evaporator which also looked to be free of dye on the bottom half (can't see top half without fuller disassembly.)

Used some A/C foam cleaner on the condenser and evaporator and flushed them out real good to make sure they were free of debris, but not a whole lot came out and they were fairly clean (evap core was a bit more dirty but still not bad).

Any ideas or directions to point me in? Don't understand why high side pressure seems so low when the low side pressure seems to be almost at what i would think "full" is considered (25-35ish?) Anyone have actual specs for our trucks so I know exactly what I'm aiming for? Thoughts on the short cycling compressor at 20 PSI? Thoughts on the pressure switch?

 

You need more refrigerant!

 

You're way under charged. The only "proper" way to get the right charge is by weight, but I've done tons of them by pressure and they worked well.

 

Totally agree. There is a seat of the pants method as well , charge till the output pipe on the evaporator reaches the same, or nearly the same temp as the input side. I will add that if the system was empty it should be evacuated before recharging at the very least, I can guarantee there is moisture in it. Most pros would fix the leak, change the dryer, evac and then recharge.

 

Pull down the system, change the orifice tube and add back the charge by weight. Most of these trucks I have worked on are right at 40psi/180psi lo/hi at 75 degrees with a evap temperature around 43 degrees.

 

That pressure switch by the compressor.... about 5 times in 20 years, I have found that the pigtail connector had gone bad, I'm guessing because if working on top on engine its easy to lay across that connector, not thinking about maybe, you're messing it up. Wiggle the wires and see if compressor comes on.... just a bit of info for those having a system that turns on & off when it wants to.

Just throwing that out there, since it happen so many times to me. Those system gremlins are really hair puller's !

 

thanks for all the advice so far gents, especially for the chart. Is there truth to the fact that the system had dye in it from the factory? Obviously I have a leak somewhere because I’m low, but it must be slow and I sure can’t find it so far.

I’m gonna see how long it holds this 20psi before I decide about vacuuming or just charging it up. Tempted to vac it and change the accumulator and orifice tube as stated above but this refrigerant is crazy expensive and it’s a rough couple months for me wallet-wise.

 

If you have a vacuum pump and a good set of gauges it isn't difficult to pulled one down and recharge it by weight based upon the sticker under the hood. I found a schrader valve on my Yukon leaking, replaced it and pulled it down as I mentioned and it turned out to be worth the effort.

 

Look at every part of the AC system you can. Condenser, fittings, and rubber lines are prime suspect. Also compressor and connections. Are any of them oily? Thats probably AC oil, indicating a leak. UV light and yellow goggles help identify UV dye if present.
Hook up your AC gauges. Is there anything in there?
If above zero, and If you have access to a refrigerant detector this is a good time to wave it around and look for a leak. R134 is heavier than air so sweep under suspect culprits. Compressor, Condenser, and evaporator core are the hard to detect items that a refrigerant detector might help with. If you don't find anything time to suck it down.

They have vacuum pumps at harbor freight cheap enough.
Recover the freon you already bought, saving that might pay for the vacuum pump.


Run the vacuum pump at 10-15" vacuum for 5-10 minutes. That should mostly dry everything out.

Close your manifold gauges with hopefully 15" vacuum and let it sit for 10 minutes.

Have the gauges maintained the same reading (held vacuum)?

If not, Pressure check to find the source of leak. I use nitrogen because it's inert, but if your going to vacuum the system anyways I don't think it's that critical, shop air will work. I pressurize to 325#, repressurize after setting for a couple minutes to account for expansion.
I use spray bottle w/ soapy water, Stethoscope, and AC leak detector.

When you get the system to hold pressure, service to the proper level of freon and chill out!!



Just adding freon to a system is stupid. There are a dozen things that will prevent an archaic system like our trucks have to stop functioning. Almost every self serviced system I see that isn't working is either empty or over serviced.

 

this refrigerant is crazy expensive

Doesn't your system use R-134a, which is ~5/can at Walmart (for the Chinese-made stuff)? I would also be wary of cheap/discount vacuum pumps. Get/borrow/rent a good one for your evacuation.

 

This i went without A/C for a long time pushed down on the pigtail and instant cold air. I was able to somewhat fix mine by bending the prongs on the switch to make better contact with the pigtail eventually i just need to replace the pigtail.

 

It's a Ford. Old green turned out no different than any other Ford owned in the past. The only way to get it done right, and save yourself the headache and frustration- replace the entire system. A patch here, and a patch there will only last so long.

 

on both the 99 crown vics, and the 02 diesel the high side schrader valve was bad and would leek out the charge over the course of 6-7 months.

it took buying a "sniffer" to find the leak.