My AC has been acting weird for the last month or so...it works great 90% of the time, but blows warmer air periodically.

Fast forward to this week. The car sat for 8 days while on vacation...my wife drove it on Wednesday and air never cooled, by 4pm it was blowing hot air.

Here's what I've done:

1. Evacuated system and pulled vacuum to -29psi.
2. Vacuum held for 1 hour.
3. Refilled system with 2lbs r134a (I believe I have rear air setup)
4. AC blew COLD and I assumed it was fixed.
5. Got in car this morning and air was hot again.

I'm not an AC guy just a DIY'r.

I have pulled another vacuum and will recharge system today. Does anyone have any advice?

 

Blend doors stuck/not working?

Can you read any codes? Need reader like GAP tool, a cheapie won't have the info.

 

Blend doors doesn't make sense I don't think. It blows cold when I put in refrigerant and blew cold for several hours...then this morning blew hot. Symptomatic of huge leak, but it holds a vacuum for 3 hours+ without even moving the needle.

 

Actually blend doors *could* make sense if there is some system fault. The heater core on these is always flowing, meaning you can get hot or cold only with a fault or failure. Also keep in mind there are pressure sensors with AC. I think two like most systems. A high and low pressure. If pressure is too low or too high the compressor will not work past its default 5% flow (its clutches, so its always pumping).

I am confused as to why you initially vacuumed the system. Can I assume you checked pressures first? If pressures were good there should have been no need to evacuate and all the other stuff. Of course you never should go by capacity. The system needs proper pressure and the amount added is in effect an estimate.

As for holding a vacuum, these systems are under pressure and not a vacuum. It actually is possible for an o-ring to seal under vacuum but leak under pressure. A vacuum test is a good test to do of course and works 99% of the time, but its not conclusive. Adding a leak dye is a best best. If you have rear AC there are several junctions that can leak (I think four total?). I can provide diagrams if needed.

You can try a self-test of the system, but its not conclusive. If there is a fault, you can find out. But it *can* give the all clear when there is a problem:

The self-test can be initiated by pressing and holding the ECON and RECIRC buttons while turning the ignition switch to the ON position.

The control module will then compare the current motor position with the values stored in the module and will indicate an error by flashing the ECON LED (light emitting diode).

If there are no errors, the LED will go out and the system will function normally.

To confirm that there are no errors, turn the ignition switch to the OFF position, then back to the ON position.

Observe the operation of the programmed defrost LED.

If there are errors present, the programmed defrost LED will flash and the system will attempt to calibrate itself.

 

I drained system because I hooked up my gauges and it showed a static pressure of 12 psi across the high and low side. I turned the car on and pressure was unchanged.

I vacuumed system and it held vacuum.

I recharged with r134a and the pressures went in opposite directions - high got up to 180psi and low settled at 25psi

The AC was blowing ice cold.

Static/equalized pressure was around 85psi in think with car off.

Next morning the pressure was back down to 10psi and blowing hot air.

I did the test you mentioned yesterday and it didn't show any faults.

 

Okay. Thats answers some needed stuff.

Sorta stumped then. The system works, clearly, when all appears well. I can only think its some sorta leak that is happening under pressure. Could even be at the compressor. I would consider a leak dye additive and go from there at this point.