F150 AC question

Status
Not open for further replies.
Joined
May 15, 2006
Messages
2,556
Location
Lakeside CA and Lake Havasu City AZ
I think I have a plugging up orifice tube on my friends 03 F150 truck, what do you think? Symptoms: clutch cycles about every 1.5 seconds, pressure on low side 25 at kick out 40-45 at kick in, high side kick in about 125-140 kick out at 175 (75-80 ambient). High pressure line from the orifice tube to firewall covered in ice, low pressure line out of evap. is warm, slightly cooler than ambient. With heater hose clamped off I get 60 degrees at low fan speed, center vent, recirc. Un-clamp heater hose and temp slowly rises to 70 degrees (about 10 minutes). During the short time compressor is on the low side drops and the high side rises much quicker than I would expect, hence I suspect the orifice tube is mostly plugged. What do you think?
 
I'm no expert but the pressures seem low according to the charts I saw. Are you checking these pressures at idle? I'd recheck at 2000 rpm and see what you get, then I'd probably add some refrigerant.
 
I assume your are referring to the high side? The pressure is climbing fast when it cuts out, I suspect it would go a fair amount above that if the compressor did not cycle off every 1.5 seconds.
 
Last edited:
I was referring to the low side pressure. The compressor might be shutting off because the low side is getting too low tripping the low pressure safety switch. I think it's supposed to go up quickly but that doesn't mean that if the compressor stayed on that it would keep going up.
 
I will certainly try adding some refrigerant before I replace the o-tube, and I am pretty certain it was hitting the low pressure cut out, but the high side rose so fast during the 1.5 seconds I assumed there was a blockage.
 
Last edited:
Has the system recently been open & exposed to air ? Has it recently had a compressor replaced ? Perhaps for a catastrophic failure ?

The 2 things that come to my mind , to stop up an O-Tube would be ice or debris from a compressor coming apart internally .

Are you getting proper air flow through the condenser coil ? Are the radiator cooling fan / fans working OK ?

I too would like to know if it is cycling on low pressure or high pressure ? I am guessing low pressure .

I think , were it mine , I also would try , very careful , adding a little refrigerant in the low side . I would probably charge with vapor , not liquid refrigerant .

Best of luck to you , :)
Wyr
God bless
 
Charge by weight then evaluate performance. When properly charged you may find the high side is way up due to condenser issues (fan clutch, dirt, missing shrouds).

A clog would cause the low side to go down until the switch trips, then stay there for a long time. Orifice tubes rarely clog. If you do have the opportunity with the system empty, definitely pull it and check for debris on the screens.

This system is showing the usual signs of low charge. If it was low, look for the leak.
 
Last edited:
good deal! Always like to hear a good ending to the story!
thumbsup2.gif
 
Status
Not open for further replies.
Back
Top