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Ford Windstar A/C pressure over 100 psi

My a/c quit working in my 2001 Windstar and it just blows hot air now, but still kicks on. Since I use the A/C a lot in Florida I figured it just needed to be charged. I bought a freon can with the gauge on it. But when I go to check the pressure before charging, it reads over 100 psi.
I’ve checked it a couple times and with 2 different gauges.
I’d really like to save money by doing this myself but I don’t want to screw anything up.
I heard the pressure might need to be vacuumed out of it before it gets charged, I’m assuming that’s something I’m going to have to take it to the shop for.

Should I give up and bring it in to a mechanic, or any last suggestions before I cave?

Thanks!

That’s way too high for the low side pressure. If you had a set of manifold gauges where the high side pressure could be monitored and showed it to be low, then there’s probably a problem with the expansion valve at the evaporator.

Bring it to an AC specialist.

Tester

I doubt the compressor is turning, look closely at the clutch when engauged. Is the center turning?

If the compressor wasn’t turning, and the system had a full charge, the static pressure of the system would be about 45 PSI on the low and high side. With a 100 PSI on the low side, the compressor is working.

Tester

The normal pressure of stored R-134A in a can or an inoperative system is about 105 PSI@ 90 degrees F.

In a can yes. Because the refrigerant is compressed into a liquid into the can. But once it’s released into the system it turns back into a gas. So the static pressure of the gas in the system will be about 45 PSI. It’s not until the compressor converts the gas back into a liquid do you see pressures of up to 300 PSI on the high side and 50-60 PSI on the low side.

Tester

? @Tester: Why do you say 45 psi? On a fully charged automotive A/C system, with the system not operating and pressures equalized, depending on ambient temperature, pressures are usually 75-125 psi both low and high. 45 psi static pressure indicates a low charge.

Every A/C system I’ve seen that was fully charged had a static pressure of about 120 PSI, give or take a little bit.

IF (caps) the compressor is actually engaging and pumping as it should be then maybe there’s a restriction on the high side or what’s actually being read is can pressure rather than system pressure due to a problem with the service port or the gauge that attaches to the port.

It would help to know for sure if the compressor is actually operating and what kind of gauge(s) is being used.

To the op, I had the same issue on my car a few weeks ago, but also have a gauge set that reads the high side. In my case I was running 85 psi on the low side and 110 on the high side, which is not enough to work. Diagnostic said bad compressor, which is what I think you have as well.

PS I am going to assume you checked the lowside with the AC on… Right???

A fully charged system will have 100+/- psi when the compressor is not operating. Those McParts store quick charge gauges are color coded to indicate the STABILIZED pressure on the low side when the system is operating properly in warm weather. At 100 psi the OP’s system likely has a full charge.

Like others have said, it sounds like the compressor is not running and you are reading the ‘static’ pressure of the A/C system. You might try jumpering the pressure swith(es) to see if it will run. 75-100 I think is normal static pressure, so it may just be an electrical control that’s failed or is sticking. Or 100 may be too high of a static pressure on the low side and may not be allowing the compressor to start–the system could be overcharged. I’d check the electrical first though.