Just bought a 2006 F350 from my company and have an ac question. Its got 113k miles on it with a new motor by Ford less than 2k ago. The ac clutch was not engaging so I checked the pressure and it was 20 psi on the low side. After 1 can (12oz) of freon the clutch would click on every one in a while. After 2 more cans the pressure is up to 30 and the clutch kicks on and the pressure goes down in about 20 seconds and the clutch cuts back off. Before I put in a couple more cans ,I just wanted to make sure I was on the right track. Should I put in some leak detector and or preventer, or just freon?

 

Unless you're in the southern hemisphere, I wouldn't be screwing with an AC charge attempt unless you are using a scale to measure an accurate charge into a fully evacuated system. Otherwise, you need a very warm to hot day to get it any closer by feel.

You're already in the ball park having added 36 oz of R134 to whatever was in there to start with. You will need to refer to the under-hood label to see what the system capacity is supposed to be for your truck as-built. My guess is somewhere around 35-45 oz.

PS Ford last used Freon in 1993.

 

You are probably getting close but the only way to know for sure is have the gas that's in the system now removed by a reclaim machine and weighed back in to make sure it's the right amount. Being that the motor was just replaced there may be a leak at one of the hoses or they never charged it to begin with. Check the hoses at he condenser and compressor to make sure the are tight but if the O rings are bad the only way to fix that is remove the gas and replace them.

Denny

 

i've done all my a/c's myself, with the proper (r134a) coolant. I bought a a/c pressure guage from the local parts store, of course you have to add in on the low pressure side. the guage has a "normal" range in it to tell u if your in the ballpark. the reason the pressure drops is that the pump is cycling the coolant which is where u want to measure it on the low side, the instructions with the guage should tell u the rest. this system worked for me all the way back to the freon days. good luck w/ your project---if you can swing the cash-- have it done by a pro--pressures w/ac systems ca get pretty high and therefore dangerous---do at your own risk

 

If you're leaking refrigerant than there's no point in continually adding refrigerant until that leak is fixed. Once a system is open to atmosphere then that system, after leak is repaired, will need to be evacuated prior to adding refrigerant for optimal and lengthy results. Moisture and any possible contaminants will be removed upon vacuum.

 

If you are just adding gas to the low side and only have a gauge on the low side you have no idea whats happening on the high side of the system. If you have a restriction somewhere in the system making it look like it's low on gas then you can kill your compressor with high pressure.

Denny

 

yes denny, thats a good point. in the 30 plus years of diy i have not run into that myself but it certainly can happen. A full pressure guage set used by a pro is definately the way to go and safer as well. and of course as texas chain ring said about evacing for max efficiency being an excellent idea. Also to little general, try not to use high vis dye to find your leak. some a/c shops won't service equipment that has had dye in it as they claim it gums up thier equipment. good luck on your project !!!

 

There is also the probability that the air gap is off on the clutch. there is a write up on how to check and fix it.. Mine was Way out. it should only be about 20 thousands
Mine was almost 60 thou out because the clutch was worn out it. kicked in and out..

 

I've got many many years doing refrigeration and HVAC an it was a PITA when I ran into a unit that had dye in it, it gets into the gauges, vacuum pumps, reclaim equipment and on your hands and if it sealed leaks why was I called

Denny

 

Dye is a problem? Seriously?

All Fords come out of the factory with dye in the system.

 

You are taking about dye added at the factory not the stuff that is added aftermarket. I have a good friend that runs a body and repair shop and I've seen more than a few condensers off of Fords and you cannot see any dye so I'm guessing that if they are using it it's the type that can only be seen with a special light. The biggest problem with looking for leaks in a system that uses R134A or any of the new style of refrigerants is the molecule size of the gas and polyester oil, the refrigerants are smaller than the oil so in small leaks oil will not come out of the system like it did with R12 and mineral oil. Any dye that is added to a system is in the oil not the gas so it is very hard to find small leaks also polyester oil does not tend to migrate into the system like mineral oil did.

There were commercial systems I converted over to new style refrigerants that never leaked until I changed them over and it was no fun tying to find leaks. It took all of us that did it for a living to get used to working with the new style expensive gases and oils.

Denny

 

Took the truck in to the AC shop today and I had put in 5 12oz cans. The AC man put in 1 more with dye that only shows up in uv light. The 1 more can was all it needed and there were no leaks. Where the hell all the freon went is anybodys guess. I found the mechanic that put in my new motor and he said he didn't evac the system. Oh well. Time will tell.

 

If you add dye it will take time to mix with the oil and circulate through the system before it shows up unless it's a very big leak. I would guess the guy that installed the motor screwed up if it holds it's charge. Take a look on your radiator support and see how much it should hold, so far you put in 4.5 lbs if the cans where emptied all the way. I he didn't get a good vacuum on the system and there is air in it when it gets hot it will start cutting off on high head pressure. If you find there is air in the system you have to remove the gas and dispose of it because when it's mixed there is no separating it.

Denny

 

I was at ac shop when the last can was put in. Tech said those 12 oz cans rarely have 12 usable oz in them.

 

I never used any gas out of a small can I always used 15 or 30 lb tanks that I weighed the gas out of so I knew exactly what I was putting in. The people that I know that work on automotive A/C units also use the bigger containers.

Denny