'01 F150 XLT
5.4L EFI
207,000 miles

First of all, Hi I'm Brian and I've had this truck since '03 @ 45,000 mi and have loved it ever since. It hasn't failed me yet, until now. Living in TX with no A/C is the pits, hopefully someone can offer some help.

I've had a certified mechanic buddy working on this issue on the side and the problem remains.

He first replaced the large hose assembly (with a non motorcraft part) due to a pinhole then recharged the system. It cooled great until the pressure pop off valve (or whatever it's called) blew all the freon out.

His first suspicion was the fan clutch, which was replaced with a motorcraft fan clutch. Next he used his a/c machine to evacuate/flush/recharge the system - problem persisted. Lastly, he cleaned the radiator and condenser fins and recharged again. The system still overheated and lost the freon.

While the freon is in the system it cools like never before but after driving it, parking for a while, then re-starting it overheats within minutes.

At this point he's at a loss, so my last option is to take it to a shop.

Any ideas or thoughts what the problem might be.


Thanks

 

First welcome. He is right, seems like the fan clutch is an excellent idea. Other than that maybe the orifice tube is clogged up? Something would have to be a restriction on the high side to make the pressures high enough to pop the relief or the fan isn't cooling the condensor down, ie it isn't condensing like it should.... Has he put gauges on it? What is the pressure when it pops? Often the valves get weak after popping over and over.

 

He said this fan clutch seems to be operating as it should now. Yes, the machine that he has been using has gauges built in and somehow calibrates to the vehicle when evacuating and recharging. It basically does all the work itself. Once recharged he said the system stays around 200psi.

Not sure what the pressure is when it blows, he hasn't been able to make it happen. It's only happened after I took the truck back. He says it should blow around 350-400 or so.

Is there a sensor on this truck that tells that fan clutch when to engage, or is it all mechanical?

 

No the fan engages/disengages with heat. Going slow, less flow and it gets hot, engages. Going fast, more airflow through it and the fan clutch cools off and disengages. It is a fluid coupling, it never locks up completely. The valves are usually set for that pressure area, he is right. Don't know exactly what these run all the time, but I wouldn't be completely comfortable with a high side of 200, if it gets hotter or the fan isn't up to snuff, it will go higher. Was that at idle or rpms up? Feel the lines, the temperature changes tell you if there is some other restriction that shouldn't be there, (IE trash in the system, this would most likely be from a compressor that was failing). It should be like this: compressor high side and high side liquid line = HOT, condenser and high liquid = hot to warm as you go to the outlet side of the condenser it will cool some, it should remain roughly the same temp until the orifice tube, low liquid, accumulator = cold (the accumulator is a filter and keeps a smooth flow past it, you don't want to chance slugging the compressor with liquid, which also makes a point, compressors must pump gas only, liquid freon destructs it and washes the oil out of it), evaporator (the part in the dash) slightly warm to hot depending on cab temp, from the evaporator out to the gas in of the compressor is cold to cool. If these temperature aren't exatly those changes you have found your problem. If it turns cold before it should in that cycle you have a blockage or very little freon. Does the clutch kick out? If it doesn't you will get two problems, first your evaporator will freeze up, then the orifice tube will shut and the pressure will skyrocket. Sorry to overwhelm you with info that you likely won't get, these temperature drops are the theory that all refrigeration systems have operated on for 100 years. This is nothing new, but a firm understanding of theory will help diagnose a ton of issues... The orifice tube has a screen on it, so theoretically trash from the high pressure output of the compressor won't recycle to the low side inlet of the compressor. Also if it has too much freon the pressures will be high, it is more beneficial to have it slightly underfilled than to have it overfilled. Sure it isn't overfilled?

 

I follow your logic on this, but didn't get a chance to feel the lines myself. I ended up taking it to a shop I trust and had a good talk with a mechanic. His first instinct after hearing what had already been done to it was to replace the high pressure switch, which is what he ended up doing.

He said every time he checked it with gauges the pressure was just fine. He drove it some and checked it; let it sit, cranked it then checked it, etc... btw the temps here in central tx are around 100 (which has never caused this problem).

After picking it up, it did fine for a day and then blew again.

I was wondering if it had too much freon in it too (before the shop worked on it). It was getting very cold almost instantly, which was great but never happened before that quickly. Only thing is, when it would blow there would be freon left which would blow out at some point later.

Any ideas?

 

The high switch cuts the compressor in and out, so ya that is possible, when it sees high pressure the clutch should kick out. He was thinking the right ideas. BTW 100 is seen here often too, we are in the 90s atleast pretty well all summer and most of fall. It does sound a little full, but your logic is flawed , you aren't alone though. More Freon does not equal colder. Freon is used because it works well with the temperature changes absolutely neccessary for an a/c system to work right, not because its "cold".

 

If the high pressure switch is working properly, it should cut out about 100 psi below the pop-off. If the pop-off is releasing prematurely and there are no other symptoms, then the pop-off is likely bad.

If the pressures were "fine", then the system was not overcharged.

 

-----The high switch cuts the compressor in and out, so ya that is possible, when it sees high pressure the clutch should kick out. He was thinking the right ideas. BTW 100 is seen here often too, we are in the 90s atleast pretty well all summer and most of fall. It does sound a little full, but your logic is flawed , you aren't alone though. More Freon does not equal colder. Freon is used because it works well with the temperature changes absolutely neccessary for an a/c system to work right, not because its "cold".-----

Gotcha, another reason why I'm entrusting in pro's to fix this problem. Thx for providing some insight, I like to be somewhat educated when I shell out hundreds of dollars to a mechanic



----If the high pressure switch is working properly, it should cut out about 100 psi below the pop-off. If the pop-off is releasing prematurely and there are no other symptoms, then the pop-off is likely bad.

If the pressures were "fine", then the system was not overcharged.----

I've been inquiring about the integrity of the pop off (especially since it's blown about 5 times now), but every time I ask the answer is usually that it's not that common. I have been wondering this too: I never had this problem before I had that autozone hose assembly installed. I just wonder if that thing in fact isn't manufactured to the exact specs of a motorcraft hose assembly. If the pop-off is part of that assembly, maybe it has been weak this whole time.

I guess it's really starting to point to some sort of blockage in the system. It's back to the shop monday morn to see what the next move is

 

What he said, really we are guessing w/o seeing my self. Personally I would stick some gauges on it for long term and see if they truly are fine. Theoretically it shouldn't overpressure, with the exception of the clutch drags and is on when it shouldn't be. Again that would show up in the pressures. I respect "leaving it to the pros" a ton of people think they are a/c pros themselves and cost themselves more than they save....

 

The high pressure cutout switch should activate around 465 psi, the pop-off around 550-600 psi per WSM.

 

well bad news, looks like I need a new compressor and condenser. The mechanic took my truck overnight and drove it with gauges, said it finally blew for him and it was around 375psi.

He knew that wasn't right so he dug deeper and pulled the orafice(?) tube out which was full of metal shavings and rubber. He said this could only be coming from the compressor, that it is basically coming apart from the inside.

At that point he tried to flush the condenser, which he said is was so full that he couldn't even flush out his flushing solution.

He also said that the dryer shouldn't need to be replaced at this point. I'm just wondering is there anything in that dryer/evaporator that could eventually come apart and clog the system back up?

Seems like now would be a good time to replace it if so

 

By the pop I figured the tube was clogged with something. Yes the metal is likely from the compressor. The rubber is likely from hoses. His prerogative, but I personally would try some more to flush the condenser. I would think either the low pop pressure was either because it was weak, or it had some metal stuck in it too....