Ac/power Issue

[BeastsNMonsters]

Hey all, I got a question.

My 04 V6 Stang's AC doesn't seem to work well. Worse, it seems RPM dependent. If I'm at idle, it works ok, and even when I'm coasting. When the engine is under load, the AC output is minimal. It barely cools at all. Any idea what the culprit is?

Secondly, fifth gear always sounds like it's lugging the engine. The other gears sound fine, just fifth is giving me issues. Looking for ideas that would be easy to repair.

Thanks in advance,
Critter

 

[wmburns]

Do you have an ODB2 scanner? If you do it would be handy to know IF the PCM is commanding the AC to turn off. This information could make real short work of your problem.

Here's some information on an affordable Windows based ODB2 scanner.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

If this were my car I would also rule out a engine vacuum leak between the throttle body and the AC/heat mode control box in the dash. What may be happening is the vacuum controlled damper motors are switching to defrost mode when the engine vacuum decreases. The AC is still putting out but you won't feel it as much since it will be directed to the windshield. This should be easy to test for by using your hand to feel the air flow to the windshield.

Look for the tiny vacuum line that runs through the firewall near the AC lines. That is the vacuum line that provides vacuum for the damper motors.

 

[BeastsNMonsters]

I'll check into the scanner. I'll need it for the wife's truck too. But as far as diverting to the dash, that's not happening. The temp and air speed are dropping, as if the AC compressor is losing speed as the RPM increases. Weird.

 

[BeastsNMonsters]

So I finally figured out what was happening here. The coil pack was going bad, possibly due to increased resistance inside it. It caused the lack of power. As the demand of the coil pack increases, the available current for the AC system decreased. This caused my AC system to slowly drop fan speed to nothing based on engine RPM. I replaced the coil, and both the power issues and AC issues resolved. Just need to replace the battery on payday. It read bad when I had the electrical and starting systems checked.