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2007 Explorer has weak AC. When driving at speed, the AC can produce reasonably cool air. When stopped at traffic lights or such, the air warms to ambient temps rather quickly.

I hooked up the pressure manifold and got:

  • AC off at idle speed: 105/105 (low/high ports)
  • AC compressor on at idle speed:70/120
  • AC compressor on at 3k rpms: 40/175

Ambient temp was 86 degrees with 65% relative humidity.

Exact measurements vary when repeated, but are all similar.

My first thought was that it was low on refrigerant, but I'm reluctant to add any when the low side is already at 70 psi at idle and 40 when at 3k rpms. The high pressure port is lower than I would expect.

This leads me to think there could be a blockage somewhere? Any suggestions?

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    Your second bullet states: "AC on at idle speed" ... Is that with the compressor cycled on or not? 70psi is very high for low side (I'm not sure, but I think 120 is pretty low for the high side as well). According to this site: The low-side should be near 30 PSI at 90 degrees Fahrenheit or less. Pressure that is too much lower or higher shows there is a problem. On a properly working system, high-side pressure will be about twice the ambient temperature, plus 50 PSI.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 9, 2018 at 0:09
  • Yes, I mean the compressor is on. The twice ambient + 50 is good info. I hadn't heard that one. I agree that the the 'low' is too high and the 'high' is too low. But it does shape up a little at driving rpms. I'll edit to be more explicit about the compressor.
    – user7264855
    Commented Aug 9, 2018 at 0:34
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    @Pᴀᴜʟsᴛᴇʀ2 it’s a good rule of thumb that seems to work. I was taught 2.5x ambient. To the OP i’m no expert on ac but it sounds like some kind of restriction or a compressor that isn’t doing it’s job. When was the last time the orifice tube was replaced?
    – Ben
    Commented Aug 9, 2018 at 1:43
  • I did have some work done on the AC a year or so ago (maybe two). The mechanic did have trouble getting it to work consistently. I know the orifice tube was replace since he showed me that the old one had disintegrated. I think the compressor was replaced too, but I'm not sure. At that point it would either blow very cold air or ambient, switching randomly. Now it is as described above.
    – user7264855
    Commented Aug 9, 2018 at 1:51
  • Is it an FS10 compressor? Too low high pressure means that it probably lost a piston seal (or more) and pumped it into the condenser, decreasing its efficiency (this can give issues similar to improper condenser airflow i.e. cold only when moving). This compressor can still pump enough refrigerant to make things seem cold even if it lost a piston seal or two, since it's a 10 piston double sided design... but it will eventually seize once the oil return rate becomes too low due to the contamination.
    – Al_
    Commented Aug 9, 2018 at 10:29

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Try checking for proper airflow at the condenser and cleaning its fins. If you have any gaps between the radiator and condenser try plugging them with dense foam. Do this and then try the system again.

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