My A/C in my 1999 F150 with 4.6L has not been cooling, so I purchased a 134A recharge kit. This kit includes the refigerant, hose, and a pressure guage.

With the engine off I'm reading 45psi in the system. With the engine running, and the a/c on MAX, the compressor kicks on when it reaches about 43psi, it runs for a second then immediately drops to below 25psi and kicks off. The pressure then starts to climb and when it gets to 43psi again, the compressor kicks on.

I'm wondering if this is normal, or am I looking at a faulty pressure sensor?

Also, if someone can tell me where the pressure sensor is and how to jump it, if I need to recharge, that would be cool too.

tia,
Jeff

 

cycling is normal. Your system does sound like it might be in need of a recharge. The pressure switch is on the accumulator. Just pull the connector and jumper it with a wire.

 

Above the accumulator is an electrical box of some sort, do I need to remove that to access the switch? It's obvious where the low side coupling is, but the switch may be hidden by this box, it's certainly not on the bottom or side of the accumulator.

 

The switch on the accumulator is the "cycling switch", not to be confused with the low pressure cut-off switch. If the cycling switch goes bad, you compressor will constantly cycle on/off, even though the system is fully charged.

 

Alright, well, I've replaced the clutch cycling switch. Prior to, it would cycle on for a second or two, then off, constantly. After replacement it cycled on for longer periods. So, I decided to put more R134a in now seeing as it wasn't pulling any in before.

So, I've got about 2 cans in there and the air is blowing much colder. The clutch is staying engaged for long periods of time now indicating that the charge is taking well.

My question now is, do I go for a 3rd can or not? The gauge is reading a constant 25psi with the clutch engaged. The instructions on the can say "when the pressure reads 25-45psi, do not add any more refrigerant." Being that it's on the low end of the range, of course I want to put more in. Should I?

Thanks in advance!

EDIT: I think I may have answered my question. According to the Hayes manual, and the sticker in the engine compartment, the R134a capacity is 33oz. With 2 cans in there, or close to it, it would seem the system is full.