Hello all,

I am troubleshooting a "warmer than normal" AC condition- (air just doesn't seem as cold as it has in the past) on a 1999 F150 5.4. Here is what I've observed so far:

Ambient temperature is 82F deg

AC register blows 58 deg. with truck going 35mph with AC on MAX and Full FAN blowing

With truck sitting and engine at 1500RPM:

AC clutch engages for 5 seconds, disengages for 3 seconds and repeats cycle

AC Clutch engages, low side pressure drops from 45psi to 20-25psi
AC clutch disengages, low side pressure goes back to 45psi and clutch kicks on, repeating cycle

AC clutch engages, high side pressure drops from 225psi to ~165psi
AC clutch disengages, high side pressure goes back to 225psi and clutch kicks off, repeating cycle

According to Ford service manual, these pressure are within range, although low side pressure is just barely within the low limit. The AC register temperature is not within range.

At 82F deg ambient, that is two degrees above possible constant clutch engagement according to the Note in the manual which indicates anything over 80F deg the clutch may not cycle. Could that explain the short cycling since the temp is so near the threshold of constant clutch engagement?

I attempted to add a bit of refrigerant, but now I'm wondering if I accidentally let a little bit out and now it has a low charge condition causing the cycling and high AC register temperature. Does this make sense?

Thanks in advance and I appreciate any info or assistance you can provide.

Mizzleman

 

You have described classic low charge symptoms. Best to have a pro with nessary tools and knowledge add freon. If you insist on diy,here's some cautions and tips. Purge air from hose to prevent putting air into system. Do not connect anything to high side unless you know exactly what you are doing. Don't exceed one 12-16 oz can unless you use tempature pressure curve method. Regardless what you see Billy Bozo do while adding freon,do not turn can upside down while charging. Instead allow engine heat from radiator fan warm can or use blow dryer.

 

Your refrigerant charge is low, see FAQs (link in signature).

 

ProjectSHO89,

My bad. I did look at the stickies before posting, but I missed that one.

I did charge the system with about half of a 12oz bottle and it stabilized at 28psi on the low and 225psi on the high with constant clutch engagement. Unfortunately, my can tap broke and wouldn't allow any more refrigerant out of the can. Bought a new can and tap and added about the other half of the can and the pressures are now 33psi low, 275F high (94F ambient) with 50F out the A/C registers.

Before I started, I had 72F out the A/C registers at 35mpg driving so this is good improvement. I did notice a small amount of residue on the low side Schrader valve cap while working on the system, so I'll keep an eye on that to see if that valve is leaking.

Thanks for the help!

Mizzleman