OT F350 Air Conditioner (Long)

I've got an air conditioner doing some strange things!

This is on an 06 F350 Superduty 6.0. The AC has been working great, no problem, no leaks, nothing tampered with. A couple weeks ago it started cooling intermittently. The air would go from reasonably cool, then warm slowly to near ambient, then back to cool.

The owner (my boss) wanted me to look at it, though I didn't have my gauges with me, just one of those low side charging hoses. So I put it on, showed low low side, I added one can which brought the pressure up to normal, starter cooling, worked for about a week.

Yesterday I looked at it, ran it while watching what was happening. Did not put gauges on (they were at home). The temperature would vary, cool to warm, the compressor was not cycling off and on, running steady. My assumption was it had leaked refrigerant and was back to where it was last week.

Today I brought in the gauges, connected them, started it up. The ambient temp was around 90*, and it had been sitting in the sun, still in the sun when I ran the test. The low side went to around 45, the high side went to nearly 500! Too much refrigerant, my first thought. I let it run, around 1500 RPM. The high side stayed way high, though it did come down some, 400-450, but it was cooling. So I let some refrigerant out (yes, feel free to turn me in to the Freon police!)

I got the high side to come down to around 300, but the low side dropped to about 20, quit cooling, cycling switch bypassed, compressor running steady. Then the high side dropped down to 150 or so. So I put some refrigerant back in. Got the pressures to level out, somewhat normal, 40 and 250 best I remember, looking good, cooling. Then both pressures dropped, low went back down around 20 something, high 200, quit cooling. Then they started back up, back to normal. But the high side needle on the gauge was bouncing, just a red blur bouncing between 250-300. Then it repeated the cycle several times.

I had to leave it, he needed to go. Later I asked if it worked, said it was working steady but not cold as it should be.

So, what's happening? No evidence of belt or clutch slipping. Condenser clean and fan working. When it quits cooling the return line gets warm, so it's not the blend door. The system has not been open or anything added (until last week) for 300,000 miles, so I can't see moisture being in the system. It has an orifice tube, no expansion valve.

Anyone experienced this? Common to this model? What kind of compressor does this have. I've seen reference to variable output compressors, Is this one of them?

Thanks!

My o8 f150 kinda did that. Only had 40,000 miles on it. Was never low on freon. I researched it on the ford forum. It was the blend door actuator. Take the radio out and they could reach it from there. Mounted up on top of the heater. $40 part plus labor. The f150's are known for it.

my 2000 SD was acting up at 200,000mi.
Just went in and did the R134 conversion, new dryer, new orifice (was in backward), vacuumed out and new R134 and oil.No problems.

The return line getting warm says there is no refrigerant flowing?? Does it have an expansion valve or orifice? 500 on the high side says the expansion valve is malfunctioning or orifice is plugged?? Is condensor in front of radiator plugged or very dirty blocking air flow?

Sorry, more questions than answers.

> my 2000 SD was acting up at 200,000mi...Just went in and did the R134 conversion...

Uh, what did you convert it FROM? R-12 was phased out in '93. (Maybe Johnny Cash built your truck one piece at a time...)

Your diagnosis on no water in the system seems sound. Orifice tube sounds like the problem but being intermittent sounds strange. What kind of cooling fan does the condenser have? Electric? (maybe quit or failing) or engine fan? (fan clutch may be on the way out).

Maybe it is the blend door,picking up heater core heat when it quits cooling.Try pinching off the heater hoses for a quick test.Are you running your engine at 1500 rpm while testing the a/c-you will get better results,IMHO.Mark

(quoted from post at 17:49:47 07/19/16) > my 2000 SD was acting up at 200,000mi...Just went in and did the R134 conversion...

Uh, what did you convert it FROM? R-12 was phased out in '93. (Maybe Johnny Cash built your truck one piece at a time...)

Click to expand...

"At this point what difference does it make?"

Hello Steve@Advance,

Classic symptoms of a dirty system. When the expansion point plugs up or very restricted, the high side goes up while the low side goes down. Usually jut happens on one side of the system though. At times the low side will go to negative pressure. I would think that it needs a good flush. You will know once you look at the expansion point. Might be just a small piece of metal or dessicant that is restricting the flow. You may want to check the condensate drain also. If is producing a lot of condensate, you have heat going in as well. I don't think that is the case though,

Guido.

Steve the blend door will not affect your system pressures :shock:
are not enough you would know it. You are not flowing enough air across the condenser.

I work on very few diesels the norm I have seen on the few I have worked on is for the high side to go way high in the first min are so of operation then the fan clutch starts to do its thang and it pulls the high side down. (don't etch this in stone I admit diesels are not my cup of tea) I don't like diesels so let them go if were anything else I would try and correct this type of condition...

Gas are diesel should make no difference the AC works the same... Maybe Bob will ring

Guido, I think you are on the right track.

I went through a bunch of Ford truck forums, most unrelated problems or no solutions...

But found one with the same symptoms. He pulled the orifice tube, clogged with sand from the dryer! He replaced the accumulator, replaced the orifice tube with an upgrade larger size, cleaned it up, charged it, so far it is working.

It would be nice to actually find a problem, but sand in the system is not what I want to see!

So, guess I'll open it up, see what I find...

I'll keep you posted.
Thanks

The desiccant bag has come apart in the accumulator. Pretty common on SD Fords of that vintage, there is a TSB. It will look like sand on the orifice. Replace the accumulator, orifice, and flush the entire system, twice. Do not flush the compressor. To be honest, I would recommend just replacing the condenser. That crap is a bugger to get out. The amount of free work I did on the last one by following Ford's TSB convinced me the next one gets a condenser at the start, I ain't going through that again. May as well replace the compressor while its apart, the shaft seal is leaking, or soon will be.

First, 1500 rpm is to high to do any pressure testing while sitting in the garage or in the driveway. 1000 rpm is high enough to tell if the fan is pulling anything. driving down the road puts lots of air through a condenser. The best way to check high, high side pressure is with a garden hose. 134a will come right down to about 200 psi quickly if the system can work.

At 300,000 miles you need to replace the whole system except the evaporator. If you pull the orifice tube it likely will be almost plugged. Now, to dispel the kitchen legend about the desiccant being what plugs the orifice, it isn't the culprit. Crap coming out of the compressor piston rings is. The desiccant won't get to the orfice through a modern condenser, the holes are just to small. The desiccant would have to leave the accumulator, get to and through the compressor and get through the condenser to arrive at the orifice tube. Won't happen. Systems that use a dryer instead of an accumulator don't use an orifice tube. They use expansion valves and the expansion valve is the next thing downstream from the dryer and will plug off from the desiccant and one good size grain will do the damage.

belt worn out; belt idler pulley grooves worn & melted. Just went thru that.

Ford says desiccant is what the substance is, why would they make that up? I can tell you have never encountered this problem on one of these trucks, the "sand" that plugs the orifice is clearly not metallic if you have actually seen it. The substance breaks down further when rubbed between the fingers. The ones I have done have not had the compressor replaced and are still cooling hundreds of miles later. Kitchen legend? Pfft!

Did a ford last week it was either desiccant are sealer. He had a can of sealer laying in the seat

If I had had a direct fit inline filter on hand I would have installed it. I stopped using those when I QUIT wasting time and money flushing.

Hello Steve@Advance,

I'll be watching for your update!

Guido.

Hello Steve@Advance,

I'll be watching for your update!

Guido.

>"At this point what difference does it make?"

Whatever you say, Hill.

We do around 200 vehicle AC systems a year. You are right about the orifice being plugged with something that is not metallic. It is teflon from the compressor piston seals (rings). Sometimes you will find little threads in the "stuff" and the grey dust builds upon those threads.

I haven't seen it all but I have seen a lot.