Hey guys - thought I'd toss this out to you all for some advice.

Have a 2007 F150 with the 5.4. Noticed this spring that the AC would no longer blow cold, and found that my condenser in front of the radiator had sprung a leak. Replaced the Condenser, and the Dryer (accumulator) along with the Orifice tube.

Had my HVAC friend hook it up to his vacuum pump for a couple hours, then refilled with R134a. Cools just fine, the problem is now that the compressor will never cycle on/off (always stays on) and will eventually freeze up on the outside of the dryer...eventually freezing the coil and blocking the flow of air out of the vents.

Keeping in mind all of this worked fine last year, I am trying to find out what could have gone wrong during the replacement of the condenser or dryer, or if I've got a bigger issue.

I can unplug the low pressure switch from the dryer and manually jumper it so that the compressor engages/disengages, so I am not sure if the pressure switch is at fault or not.

I am going to have my friend come back by and recover the Freon, hook the system back up to the vacuum pump again for a longer duration, thinking there may be moisture in the system that's causing it to freeze up...but beyond that I am a little stumped.

Thanks guys!

 

As a side note, the orifice tube I replaced was the $1.99 OEM replacement from O'reillys... I noticed that they also have 2 higher priced ones that are labeled as Automatic Adjusting. One for severe climates, one for normal.

Not sure if that would make any difference?

 

Hey PartsChaser, I just replaced my accumulator this afternoon and was wondering what that switch on top did. According to my 2002 service manual it is called a A/C cycling switch. "The A/C cycling switch senses pressure in the suction accumulator to control operation of the A/C compressor". If you can jumper it and control the cycling of your a/c clutch I would say that's definitely what your problem is. If your 2007 is anything like my '02 it should be an easy fix too, it's just a schrader valve and you can unscrew the old one without losing any refrigerant and screw a new one on.

I would try that before I would evacuate the system again. Here is a description from my manual :

The A/C cycling switch is mounted on a Schrader valve-type fitting on the top of the suction accumulator.

-A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem.
-This allows the suction pressure inside the suction accumulator/drier to control the operation of the A/C cycling switch.
-The electrical switch contacts open when the suction pressure drops, the contacts close when the suction pressure rises. For specifications regarding operating pressure(s), refer to Section 412-00 .
-When the A/C cycling switch contacts close, the A/C clutch field coil is energized.
-When the A/C cycling switch contacts open, the A/C clutch field coil is de-energized and compressor operation stops.
-The A/C cycling switch will control the A/C evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing.
-This prevents icing of the A/C evaporator core and blockage of airflow.
-It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.

 

Replace the pressure cycling switch and try again. If it sticks closed, you'll always ice up the evaporator.

 

Its definitely worth a shot. Thanks guys!