Question
Business Truck
My Ford 2003 F-350 air conditioning freezes up. I have spent approximately $2000.00 over the last 3 years trying to have it repaired with 3 different mechanic facilities with the local Ford dealership being one of them. Parts that have been replaced are low pressure and high pressure sensors and new compressor. I do not know what other parts have been replaced but this has become frustrating to say the least. The system has been charged and recharged at least 3 times. When the unit freezes up the fan starts to blow either warm air into the cabin or gets blocked out completely.
Today it stopped getting cold completely.
Any suggestions that I might refer to my mechanic would be appreciated.
AnswerBeautiful truck. And really nice trailer!
An Evaporator that turns into a block of ice can be frustrating for the technician and the client. I think we need to back up, understand why this happens and then look for some possible solutions. I have run into this a few times on Ford trucks and I will explain to you what I found, how I solved my problems and maybe the automotive gods will smile on us and allow us to repair yours as well. I am going to ask questions along the way and label them with a number. Answer them to the best of your ability. This is going to help me diagnose the problem or modify the system to work properly.
1. When the system is no longer removing heat from the air and the evaporator is frozen over is the compressor still running? When I say running I mean is the clutch engaged. The compressor hub always spins with the belt but there is a magnetic clutch that pulls the hub in to actuate the internal compressor. When the system has stopped running is the compressor still trying to pressurize the refrigerant. This is the first and most important question.
This is going to sound crazy but we need to figure out what is happening first. The end result is an evaporator that resembles a frosty block of ice but there is a sequence of events that causes this to happen and when we figure this out we can move forward some more.
2. Ask your tech (unless you already know the answer!) if the evaporator is freezing internally first or externally first. If he knows his AC he will not give you the "what the heck?" look and answer you directly. If he didn't know there was a difference you can educate him.
External freeze up occurs when the evaporator cannot effectively displace the condensation on the outside fins and the water forms ice, it restricts the flow of air that can pass through it, which gives the illusion of the air not functioning. Some things that can cause this are excessive humidity in passengers compartment, inadequate air flow over evaporator or dirty evaporator core.
Internal freeze up occurs when there is too much moisture inside the system. The symptoms of internal freeze up often surface after extended highway driving. The volume of air stays constant, but the temperature of the air gradually rises. When this freezing occurs the low side pressure will drop, eventually going into a vacuum. I have seen this happen after a customer left his AC lines off the compressor while waiting for a new one to arrive. It was a very hot and humid week and ambient air intruded the system and contaminated the drier and lines.
So lets find out what came first, the chicken or the egg. You answer the 2 questions I asked and I will continue. Please offer as much detail as you can. I would also like to know what engine size is in the vehicle. I am assuming it is a 5.4 gasser.
I had a few cases of evap freeze over in the last year or so on Fords. They were very very frustrating but all got solved eventually with some thoughtful and methodical diagnosis.
There was a F250 in this spring and it was especially difficult to repair. It came from another shop that had jammed it full of new parts to solve but would still freeze over almost exactly 30 min into a drive cycle when ambient humidity was above 30 or 40 percent.
It was a mobile dog grooming business and the owner had ST bernard that sat in the front passengers seat all day with him. I never saw the dog but I saw the hair all over the seat and a picture of the dog on the sun visor.
You see, when you put you AC on Max what you are doing is diverting airflow intake from outside to inside. Basically super cooling the already cooled air in the cab. When this guy was on Max it was dragging dog hair onto the coil. Why this is bad is because it gives moisture a place to condense and the hair would not let it drain out so it would start a chain reaction of EXTERNAL freeze over.
3. Is your system draining water on humid days? A great deal of air condition processes dehumidification. If the water is in the air it will condense on the coil and then when the droplets get heavy enough they will fall, collect and then drain out the bottom. ALL ac systems produce water in high humidity. ALL of them do.
Another Ford product I had once was very simple. It was undercharged. 4. Exactly to the ounce how much refrigerant are they putting into your system? I think its about 40oz but I will recheck when you tell me what is installed.
So answer those questions and get back to me. I don't have alot going on this weekend so I will be replying very quickly. Once you have answered those four questions I will readjust the attack plan and proceed. Good luck. hope hyou found this helpful!
Wayne
