When I test drove this 2004 Ranger Edge 4.0 I purchased about three weeks ago it had mucho AC cooling. So much so I had to turn it way down.

Today, when I could have used it, the AC has gone south. There is very moderate cool air coming out even on the turbo setting. Was actually better with the AC off and the windows open when the truck was on the road.

I got a sick feeling thinking maybe the dealer topped off the coolant knowing it had a leak but I have a push-on plastic coolant gauge and it is reading "filled" into that blue area about 25% of the way with the truck at idle and the AC on. The compressor is cycling on and off... mostly off, though. Not sure if that is normal or ??

Your thoughts? What to test?

 

I have seen compressors kick on and off like that because they are low on coolant,,, run it a few miles with air on then pop the hood go to passenger side and see if the top curved pipe is cool to touch and sweating,,,could be a number of things,,, could be air gap on compressor,,, could be the orifice tube,,, could just be low on coolant,,, i would get a good gauge on it, before doing anything else

 

Has the a/c quit working or is the air only coming out the defroster vents? Could be just a loose or broken vacuum hose.

 

So I now know...

Cycling does mean low refrigerant. Sometimes if too low the compressor will not come on at all. There is a pressure switch next to the low side port that measures the pressure. If you short the leads (2 wire system,only) in the female connector you can force the compressor to run. Helps when adding more R-134 so that it will draw it in.

I'm going to try a product called Blue Devil Red Angel Leak Stop. The version for $40 with the low side fitting tube. It comes with UV dye so should show the leak location before it fixes it so I will know where it is for the future.

Then, I will top off with more R-134... the straight version with no additives... until my gauge reads 40psi for proper level. I will hope for the best. If it gets me through the season I will be happy. Come winter I can spend the time to replace parts if need be.

 

Lets think about this some more.
Seeing as how this seems to have come about suddenly, you've measured that the low side psi seems ok & the compressor is cycling, so can you Hear, or observe the blend door in the cabin air duct work??? If its arm connection is broken, or breaking(which is a common problem on Fords), it can stick open & bleed hot air in the mix, or if the cabin control system has developed a vacuum leak, as has been suggested, maybe it's defaulted to the "defrost" mode & if so all cooling will be directed to the windshield vents???

If as you say the purchase is only 3 weeks old, unless the purchase was "as is", surely you got some kind of warranty & if so, consider making this the selling Dealers problem.

More thoughts for consideration, let us know what you find.

 

Low side is actually around 20psi when the compressor turns on. Should be 40psi if normal. These push on testers take the reading at the moment they make a connection then lock the needle. Hence, the reason I got the initial OK reading. Holding in the reset button allows the needle to travel up and down with the cycling. This is why I suspect it is low on refrigerant.

AFAIK the compressor should not be cycling if the cabin is set to full fan and full AC. It is seeing low pressure and that's the reason the pressure switch is kicking it back off.

Three weeks is more than enough time for any refrigerant added back then to leak off to where it was prior to the sale. This dealer is an A-Hole. I am done with them.

 

OK, well then look around the compressor seals, or line fittings for refrigerant oil signs at the leak & decide what to do from there. If no oil signs, add the 134A with dye & see if it'll show anything. I'd not add a sealant, as it could cause other problems you don't need.
Let us know what you find.

 

scooterspal:Low side is actually around 20psi when the compressor turns on. Should be 40psi if normal.

Those numbers will vary, depending on ambient temperature. The pressure in the evaporator should be barely below 32F boiling point pressure for the refrigerant. If you take the pressure lower, you will frost the evaporator.
If the ambient temperature is low, the compressor should cycle when the pressure gets too low, to where it would freeze up the evaporator.

If the gauge will not provide a constant reading, it is IMO, a recipe for disaster. I would like to see the package documentation that gives a reason for a 'one-time' measurement. Any professional set of gauges will read constantly. There is a reason for that.

I would not pick '40 psi if normal' as a rule of thumb for the low side pressure. I'd look up the vapor pressure for the refrigerant used.
tom

 

^+1 & like tomw's post!!!

 

There are two pressure switches; a low and a high. The low opens if the freon pressure is too low - such as when the system has a leak, and the high opens if the pressure is too high - if the system had blockage for instance, to make sure it doesn't have a catastrophic failure. Pressures vary based on ambient air temperature, so this becomes an important part of determining where the pressures should be.

Take a look at the attached charts; being able to monitor the low and high pressures for the appropriate outside temp are an important part of troubleshooting.

Know one thing for sure - "topping the system off" will keep it working for a while if you have a leak, but each time you do this you introduce air. Eventually you will get enough air in there taking up space where Freon should be and it won't be able to cool properly. If you only add Freon once a year you'll probably get a few years out of it, but start adding to it every few weeks and it isn't going to last long.

 

I like both Tomw and Talltruck posts,,, this information should be put where it is easy for new members to find,,, and junior members like me,,i knew about the low pressure switch but not the high one,,, and talltrucks pressure chart is just way to handy LOL,,,, great information there fellows,,, keep up the good work

 

^+2 on Talltruck's post, that's useful trouble shooting & service info, so I like it too!!!

 

That's the beauty of this site, everyone sharing what they can. I keep those images on my phone and use them every time I'm working on an AC system so I know where the pressures should be. I've gotten so much help from here and I'm just glad to share something back.

 

Correct. My low switch is the one that is tripping and shutting off the compressor.

 

Well, it is the exact center of 25psi and 55psi. The two extremes on your chart.

Yes, it can vary with outside temperature, correct. At 80 degrees... about the point most of us would be turning on the AC... the pressure should be 40psi according to your chart.