Automotive Air Conditioning Information Forum

mk378 wrote:You may have a bad TAO sensor, I don't know how that would affect the rest of the system.

It looks like there isn't actually a vent temperature / TAO sensor anywhere. That number is a calculated value based on the other sensors' data.

I redid the same test as before on a hotter day (88F and sunny) to see if I got similar results.

1. Ambient pressure with A/C off: 105 psi
2. Turning A/C on at idle: immediate drop to 65 High, 15 Low.
3. While at idle: High wobbled and climbed to 80, Low would climb to 24, then lower to 16, then back up again. ???
4. Increase to 2000rpm: High remained around 80, Low dropped to 11.
5. After a minute at 2000rpm: High 95, Low 14.

Same conclusion as before? What is the cause of the Low going up and down while sitting at idle?

I'm more interested in why the high side drops lower than the static pressure. That should never happen unless you're measuring wrong (couplers not fully engaged, manifold wheels opened instead of closed when measuring pressures), or there's a restriction between the compressor and the high port.

High discharge pressure and really low suction pressure normally indicates a restriction on your discharge/ high pressure side. Your filter drier / desiccant sock probably broke open and clogged your condenser. When the high pressure side is discharging into a restriction obviously the pressure goes up. But on the suction side it eventually runs low on refrigerant, if its restricted enough it’ll go into a vacuum. Sometimes restrictions can be hard to diagnose, it could be the expansion valve not opening enough. But your low side pressure would be higher, and normally theirs freezing up close to the valve.

I agree with bohica2x0. If the shop evacuated and recharged it to spec and your high side is still very low, like you're seeing now, the compressor is shot.