On my 2006 F-150, 4.6ltr V8, XLT, the air starts out cold and gradually goes to warm or even close to hot. After sitting for a while, like over night, it starts out cold and gradually gets warm. I bought a can of Freon and proceeded to add it, but the gauge pressure is nearly pegged at the high end. I bought a set of gauges and the day I got them, second time I tried to connect to the truck, the low pressure connector flew apart. So I don't have a gauge set yet. There was a couple of times, previously, the temp went up then back down. This led me to think the blend door actuator was bad. But since it starts out cold every time, then I don't think it is the blend door. I have ordered another set of gauges, so I can at least see the pressure differential. Does anyone have an idea of what could be wrong with the system?

Thanks.

 

Is the engine cooling fan pulling enough air. Maybe the fan clutch is bad. Spray the condenser with water while the AC is on. If the A/C works better, you're not getting enough air through the condenser, which can caused by a bad fan clutch or by a condenser packed with mud/debris.

 

start the truck and turn on the AC... look at the compressor to see if the clutch is engaged.. Rev the motor to 2000 RPM and hold it there... the clutch should stay engaged for 20-30 seconds, then cycle off for 10 seconds, then back on.. etc... If it does that, then you have enough R134 .. If it cycles off too fast and will not stay engaged, then you are LOW.. ......... pressure reading is a good idea...dont give up on the blend door, still a possibility.

 

Based on the sparse information provided, it is unlikely that the issue is related to the blend door, it's more likely the clutch isn't engaging properly as the system operates for longer periods of time.

Focus first on the operation of the refrigeration system. Observe the operation of the compressor clutch for proper engagement. Your observation of the can's gauge being pegged indicates that, either you were on the wrong port (shouldn't be possible with correctly manufactured connectors) or that the compressor was not operating and you were reading the system's static pressure (ambient temp in degrees F multiplied by approximately 1.1 or so).

If the clutch is operating, proceed to use the "fingertip test" on the evaporator inlet and outlet lines to see if there is refrigeration activity. A properly operating refrigeration system will have very cool (30-40 F) lines both going in and coming out of the evaporator core.

Clutch on/off cycle time is variable and is dependent on a number of factors. Under normal operation across a range of conditions, one might observe anything from 10% to 100% duty cycle. See charts in factory service manual.

Suggest reviewing the HVAC FAQs linked to in my signature. Although originally written for the previous generation of trucks, everything there still applies to the OP's truck.

 

So here is what I have at this point.
Static pressure at 90 degrees was 88 both sides.
Running pressure 45 low, gradually climbing from 145 up 410 when I shut it down. I suppose the high pressure switch would have shut down the compressor. That is what is happening. After the pressure switch cuts off the compressor, the air gradually gets hotter in the cab.
Watching the gauges, The low pressure side gradually climbed as the high pressure side started to go down. When they both got to around 150 I disconnected and closed the hood.
This system has an orifice tube, not a TXV. I suppose this is telling me that I have an obstruction in the condenser? What other tests can I do to really isolate the problem?

 

yea... there is no way the high side should go to 400 psi ... something is plugged.

 

Well, it could be a high side restriction but it could also be insufficient heat rejection by the condenser. The quickest way to diagnose the second condition is to hit the condenser with the water stream from a garden hose and see if the high side pressure drops or not. If it drops like a rock, then it's insufficient airflow as Bent6 was alluding to.

 

I had similar issues. Kinda cool air, but not much. It would start out cold, then go warm. I took the clutch off and adjusted the clutch to spec by removing the only washer left and it's been cold ever since. Not exactly ice cold, but good enough for a 95 degree day.

 

Could be your orifice /filter is clogged but one wonders where the plug came from . Its not hard to change and they are cheap .

 

The only real repair that I have had on the 2007 F150 5.4 4x4 is air conditioning. Apparently the compressor was dragging down the engine to the point of service engine soon light on. A complete Motorcraft a/c kit was recommended by our trusted independent shop and that was a year ago. The truck has been running fine since and the a/c is working well. This is not a cheap repair and may be somewhat common for this generation of F-150. My truck had the issue at about 165,000 miles.

 

Hmmm..... I've actually never seen it nor have heard of it. Or, at least, not described like that. I've seen and experienced plenty of pulley bearing and compressor clutch failures, though. In any event, different set of symptoms than this thread is related to.

 

Of course you should put a new dryer in with the orifice it will have to be vacuum purged anyway . If your system is going as high as 410 it can rupture the hoses that are designed to do so in an accident . Plus at one point it gets dangerous ,that's why the hoses are designed to pin hole out to release it .
You can tell a lot when you pull orifice tube as to whats clogging it . Compressors can start to fail and clog it or hoses can start deteriorating , bad dryer can let desiccant start getting loose in system .
Has it been in an accident .
Anyway system may need purged/cleaned . Lets just hope some minor stuff blocking orifice. moisture/ice in system ? Some people try to open system and quickly put it back together to avoid pulling vacuum --that doesn't work wet air enters immediately . A good vacuum actually boils water in system and then sucks it out as vapor .All air contains water so purge hoses when filling .to keep from injecting air .

 

Uh, no, they're not. There is a blow-off valve on the high side that is designed to pop if the pressure exceed s somewhere between 450-550 psi.

 

I know some used to have the hoses that do that . Your right I do not know that these do . I only do my own hvac . The kids and all the rentals too. I think this one has a high pressure relief on compressor .My ac on my 05 has never failed at 230k

 

I think I'll order the parts and replace the compressor, dryer, condenser and orifice. When I have it disassembled I'll try to figure out how to clean out the evaporator. I don't think I can get it out without removing the dashboard. Haven't looked. In any case, if something is clogging the system that something came from somewhere. When my wife's F-350 quit cooling she took it to a shop (I was working out of town). They said it was her compressor. I came home and ordered a compressor and orifice and took the system apart to replace it. There was something that looked like straw or hay trapped in the orifice. I have no idea what it was. Maybe some kind of liner that came off the inside of the pipes. I blew them out real well. But I should have probably replaced the dryer and maybe found some way to clean out the condenser and evaporator. So far no problem and the AC is cold. My truck has 308K+ miles on it. So the hvac has done a lot of work.