Very high pressure reading on the low pressure port on the a/c system

My a/c is barely cooling and so my first thought was that I was low on freon. When I checked it with one of those autozone gages that has a connector on one end and a fitting for a freon can one the other the needle on the gage pegged out in the red zone showing very high pressure.

This is the original untouched factory a/c system on an '08 340,000 mile truck and nothing has been touched on it so no telling what all is wrong with it.

Do I need to get it in mind to just replace everything?

 

I think you should put a real set of gauges on it before you do anything

 

Or take it to someone that has the tools and expertise to diagnose it properly.

That gauge you used is garbage for diagnosing anything.

 

Like they said, get some real gauges.

But also if your compressor isn't kicking on, the low pressure port will read very high. You need to get the compressor to kick on or you won't be able to properly fill the system. Once it does, your pressure will read as expected (likely very low if your compressor won't kick on)

 

The compressor and clutch is kicking on and it's blowing semi cool air but I'd say it's only cooling about 1/4 as cool as it did last season. I know it has a slow freon leak and I've topped it off several times with one of these autozone fillers but never before have I had a pressure reading on the gage this high. Maybe it's just this cheapo throw away gage like you said. I just hate paying out the wazoo for a nice gage and manifold set that I will only use 3 or 4 times.

 

Nice set of gauges can be had for less than $100 and it'll pay for itself just in labor cost if you take it to a dealer or some other shop to have it diagnosed.

 

As noted, you need some real gages. I suspect your high reading is while the compressor is cycled off, in which case high side and low side will be about equal and depend on ambient temperature. You could be correct that you are very low on refrigerant. If that is the case the compressor will not run for long before it kicks off due to low suction pressure. So, you might get some coolish air. If you have a set of gages, you can observe this happening. The end case is that refrigerant gets so low that it won't kick on at all. Then you might need to jump the relay to add more refrigerant. But first, find and fix the leak.

 

Autozone or others will rent out the gauge sets in a lot of places. Pay a deposit and then get a refund when you return them.

 

You can not acurately charge a system with only low side pressure, it's not even ideal to do it with a manifold gauge set but it's much more acurate if you know what the pressures should be vs ambient temp.
Another problem with those quick charge cans is many of them contain stop leak which will absolutely wreck an A/C system if any air or moisture ever gets in.