Not sure where to go from here

[mrledee]

Hello everyone, and thanks in advance for your input.

I have an '06 F-350 diesel that's been having some a/c trouble. Gradually, the system started decreasing its ability to produce cool air. Fans blow, but I noticed the compressor was cycling on very frequently (every 3-5 seconds). I could tell that it is cooling somewhat, because there is a slight air leak by the fan motor under the hood and I feel cold air coming out, but none of the lines under the hood feel cold.

I bought a set of professional gauges and a vacuum pump. After testing the system, I saw the low side was going between 20 and 60psi and the high side was zero. Strange (possibly didn't connect correctly the first time thinking back). Based on what I found, I read that the problem could be a clogged condenser. I had the system drained and replaced the condenser and the orifice tube, vacuumed the system and it held vacuum overnight. The next day, I added the correct amount of refrigerant and it started blowing cold for a few minutes but then got warm again. The compressor turns on and off frequently (low side between 20 and 40 psi, high side between 210 and 240, ambient temp 75-80F) and a/c is barely cold. At this point, I am confident that the system has no leaks and the correct amount of refrigerant is in the system. When my a/c first started to feel warm, no changes were made to anything. The system was untouched. Any suggestions? Was thinking about expansion valve or maybe pressure sensors???

Thanks

[bohica2xo]

There are a couple of switches & sensors, but looking at your pressures those appear to be working.

The thing that sticks out in your post is very poor condenser performance for those low ambient temperatures. Generally we would go right to blaming the clutch fan for that. Your Super Duty has the electrically controlled fan, which is usually a reliable unit, so here are some additional tests & questions:

1) Were those pressures taken at idle or 1500 engine rpm?
If those were idle tests, reconnect the gauge set & test at 1500 engine rpm, with both doors open & the cabin fan on highest speed. Record high & low pressures as well as the ambient and vent temperatures.

2) To check the fan airflow / condenser performance, with the system idling, grab the garden hose & spray a light mist of water on the condenser while watching the high side pressure. How far does it drop? Increase the spray to a good shower - how much does it drop then?

Finally, how much oil did you add back to the system when you replaced the condenser?

Have you read the codes on the vehicle recently?

[mrledee]

Thanks for your reply. So as of yesterday, here's what I figured out.

I removed the cover from the evaporator and saw that some of the fins were clogged. I cleaned out the coils with coil cleaner, let it dry, and ran the a/c. It was strange that prior to doing this, the only a/c line that felt cold to the touch was the one after the orifice tube going to the evaporator. After opening the cover, the other lines now felt cold (though not as cold as they should be). I think the cabin air feels a little colder, but not much. Upon touching the evaporator, only certain parts feel cold to the touch.

This afternoon, at 80F, my low would cycle between 20-40psi, and the high would be sitting right around 150 (+/- 5psi or so). The compressor only kicks on for about 1-2 seconds and will stay off for 10-15 seconds (not sure if there is too much or too little freon).

Do you think the evaporator might have an internal clog? What are your thoughts on replacing it or the dryer?

[bohica2xo]

On a 12 year old vehicle with a major part replacement we generally replace the dryer at the same time.

It looks like your system has a leak. Your pressures & cycling indicate it is low on charge.

Again, how much oil was added when you replaced the condenser?

[mrledee]

When I changed the condenser, I added about 1 oz of oil. I was thinking of adding some more freon tomorrow. All of the pressures I listed previously was listed at idle.

I don't think my system has a leak (unless it is a very small one), because the night before I first recharged it the pressures held steady for over 12 hours. If the recharge doesn't work tomorrow, could it possibly be a sensor?

[Cusser]

This afternoon, at 80F, my low would cycle between 20-40psi, and the high would be sitting right around 150 (+/- 5psi or so). The compressor only kicks on for about 1-2 seconds and will stay off for 10-15 seconds (not sure if there is too much or too little freon).

Those pressures are low if measured lie at 1500-2000rpm. Add some refrigerant. NO SEALER. NO REFRIGERANT CONTAINING SEALER.

[mrledee]

The pressures I measured were under 1000 RPM (at idle). What would be my target pressure @80F? Should pressures be measured at idle or 1500-2000RPM)?

[bohica2xo]

Your system started out short cycling with high pressure on the high side.

A few days later it is short cycling even worse, and the high side is 100 psi lower. It has a leak.

You had enough refrigerant in it at first to see 240 psi @ 80F ambient at idle a 3:1 P/T ratio that says poor condenser performance / air in system / way too much oil in system.

You only added back an ounce of oil, so cross off too much oil. That leaves air in the system & the condenser.

What sort of vacuum pump did you use? How low did you pull the system?

You have had issues with service connections already, are you sure you were properly connected to the system during evacuation & testing?

.

[mrledee]

The condenser was replaced a few days ago, so I would hope the condenser is working properly. I don't think there is a leak, because my gauges have been connected to the truck for days, and every morning when I check the truck before starting it up, both the high and low are at 100psi. When I pulled the vacuum on the system before charging it, I waited until the next day to check the pressures and the needles on the gauge didn't move at all.

I find it strange that the line immediately after the orifice tube is ice cold, but for some reason, it seriously loses it's cool going into the evaporator. I don't know if the issue is the evaporator. Being that the pressures look good, what would cause the compressor to be turning on for only a brief moment? System clog? Sensor?

[Cusser]

every morning when I check the truck before starting it up, both the high and low are at 100psi.

I don't see where such readings are of any value. Just shows you have some refrigerant in the system, in equilibrium between gaseous state (the pressure) and liquid.