AC leak?

[Pmeadows]

I have a 2014 Chevrolet Silverado 1500 lt 4wd. I've always had issues with the AC. I thought it was due to a factory issue I kept hearing about with a ground under the dashboard ( may still be a separate problem). Anyway, this year the AC was working okay but then stopped blowing cold air. I checked the freon level and it was low. I added freon and it worked great for about 2-3 weeks and then nothing but hot air blowing. I crawled under the truck and saw a lot of oily residue/buildup on the AC lines directly behind the bottom of the radiator. I've seen no oily stains in ir on the radiator area. I added freon and sprayed soapy water on those lines and found no leaks. I sprayed soapy water on the block where the lines go through the firewall and instantly had rapid bubbles but from behind the lines where the gasket is between the block and the firewall. Could this just be cabin pressure? I had all four windows down and had the AC on high and recirc. I've attached a screenshot from a short video.

[Cusser]

Disclaimer: I'm NOT an AC professional. I'm in Arizona, do have some experience though.

I checked the freon level and it was low.

Actually, the R134a amount can only be checked with a special recovery machine that pulls out the refrigerant and WEIGHS it. Trying to guess refrigerant level by pressures is just a guess.

I added freon and it worked great for about 2-3 weeks and then nothing but hot air blowing.

This would appear to align with a refrigerant leak. I sure hope that you only added pure R134a because if you added refrigerant containing a "stop leak" chemical, you may have created permanent damage. And many shops won't work on vehicles with stop leak chemicals in their system.

I have a 2014 Chevrolet Silverado 1500 lt 4wd.

We have a 2014 GMC Yukon (4 years now) and although our only AC issue on it was a bad in-dash actuator, these vehicles are known for having faulty AC condensers, leaks on the driver side.
See https://www.youtube.com/watch?v=k0-WmsJHPrs

[JohnHere]

IMHO, the comments from Cusser are right-on.

In addition, I would like to add that if you live in an area of the country that uses chemicals on the roads to melt ice and snow in Winter, you probably have additional pinhole leaks in those lines routed down low and behind the radiator. If the metal lines are covered with foam insulation, the leaks would be even harder to detect, although the oil stains strongly suggest leakage down there as well.

I don't think that it's "cabin pressure."

When you say only hot air is blowing, do you mean heated air or ambient air coming through the A/C vents?

I haven't seen a Technical Service Bulletin about the ground under the dash, so I have no first-hand knowledge about that.