Junior Member
old Ford
I have a problem with a 20 year old Ford 150 5L. The AC unit works for about ten minutes then shuts down not producing cold. Shut it off for ten minutes and it blows cold again. The coolant is tested to be good, the electric clutch is also working. What may be the problem.
Regards M.I.Twice
Senior Member
It's low on Freon. When most of the remaining Freon gets pumped to the high side, the pressure switch on the low side opens to shut the system down.
It's possible the switch itself is defective, too. I've had to replace the one on my Silverado twice in eleven years.
Senior Member
Since the refrigerant tests good then it sounds like moisture in the system, most likely there was/is a leak and the system leaked down then was recharged. It may be that the system was repaired and then recharged without proper vacuuming prior to the recharge but whatever happened it sounds as if moisture has entered the system. You will almost certainly need to replace the filter/drier and have the system properly vacuumed to remove this moisture and while under vacuum it can be determined if there is a leak or not. You really need to take it to a reputable shop (be careful there are a LOT of AC ripoffs out there!) and find out for sure what's wrong but moisture is the most common reason for what you are describing. What happens is even a tiny amount of moisture in the system will freeze when you turn on the AC and block the proper flow of the refrigerant causing the cooling to stop, when the AC is shut off the water will thaw and refrigerant will start to flow again until it again cools enough to freeze the water and the whole cycle starts over again. The filter/drier unit will be saturated and will have to be replaced and vacuuming the system before recharging is a MUST!
Last edited by radkins; 09-09-2011 at 04:28 PM.
Senior Member
Both good points but it doesn't take 10 minutes to pump the refrigerant to the high side. I would lean toward Radkins diagnosis without knowing any history of the AC system. If it's 20 years old, the system is/was R-12. If it was converted to R-134a, it's a crap-shoot because there's no telling what was done or when. The Sanden compressors will pump their guts out, bless their hearts, and you could be seeing the first stages of a failing compressor. As the teflon rings wear, the pieces will clog the system.
Knowing how the shop tested the refrigerant to be "good" would go a long way. Your best bet is to take it to a shop that specializes in AC and not a general repair shop.
Senior Member
Only works for about ten minutes, then if you shut it down it will work again in a bit? You mentioned that you had it checked and I'm guessing it had sufficient refrigerant not to be a concern to the professional who checked it.
What geographical region do you live in? Sometimes high temperatures and high humidity can make an A/C unit quit working when the evaporator core freezes up. Shutting it off, and allowing the ice to melt usually restores function to such a unit. BUT, it's not supposed to lower the core temperature below 34 degrees F.. This would lead me to suspect a low refrigerant charge or an improperly set expansion valve, which regulates the core temperature.
Converting over to R-134a is questionable at best, since R-134a is quite sensitive to volume in an A/C system, and many conversions are undercharged regularly.
As mentioned earlier, on another thread, GET A PROFESSIONAL to look at the system...don't screw around guessing this & that....
No good deed goes unpunished.
Senior Member
I would almost bet it's system moisture, I have seen this a bunch of times. Recharging repeatedly from small cans or even using pro equipment without purging the equipment hoses can induce enough moisture into the system if it's been done several times. The most common cause is changing a component such as a line or opening the system for any other reason and then recharging without vacuuming first can cause this problem. Happens all the time however even when done by people who should know better, they change a hose or compressor then just charge the system and expect everything to work properly.
Senior Member
The first problem is the 20 years old . Time foe a new one . nothing last for ever. Expectantly old stuff.
Every Mans Work Is A Portrait of Him Self
http://sites.google.com/site/machinistsite/TWO-BUDDIES
Senior Member
No. Moisture inside the refrigerant lines can't freeze, due to the high pressure and temperatures is encounters...
The only possible way water could freeze would be if there was at least a pint or more in the lines...But, with that much water, the system would be rendered permanently inoperable in a matter of minutes
No good deed goes unpunished.
Senior Member
Where do get that? Pressure at the input to the evaporator can be 10psi or less and the temperature is well below freezing. Unplug the fan and see how fast frost forms on it just from the humidity in the air. The same thing happens INSIDE if there's the slightest accumulation of moisture.Moisture inside the refrigerant lines can't freeze, due to the high pressure and temperatures is encounters...
Senior Member
Im sure it can't.. On the high pressure, hot side.Originally Posted by saltmine
Now, On the low pressure, freezing cold side.. thats another story.
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