Scrh1

I know this may be a longshot, have you checked your front fans and resistor packs on them? If bad the ac won’t work. I found this out a few summers back on 05 degree day.

Ben8jam

I have cleaned out the front radiators (bumper off) and confirmed they blow, but haven't checked the resistor packs (i have to admit, not ever sure what those are). The AC did start to get cold as it got closer to the end of the first can, so I suspect freon is part of the issue, but I am really going blind here. Initially reading online, it seemed so straight forward to recharge system... turns out there's math involved!

Scrh1

If you have durametric you can turn them on and off. Other test is turn on ac. Go to front of car and see if the fans are sucking air. If the fans are our There is a diy for the resistor packs or you can buy the whole fan assembly.

allcool

Don't worry, there is a hi&low pressure switch that will shut things down if needed.
Lowside line should be cold when fully charged.

theprf is correct, that charging a maybe leaking, unknown current charge state without full view of hi&low side pressure is less than ideal. But can be done successfully to get you in the ballpark..
I'm hoping maybe we can get your ac into the ballpark of operating temps. What now is the center vent temp when driving at 2500rpm or so...?
You can get small digital thermometers cheap of Amazon.

If you have a substantial leak, theprf is also correct in that a professional would do a leak check when he finds a system low on refrigerant. It is the right thing to do as a professional will have all the equipment needed to do this. On the other hand, we are a diy project here, and have no idea how long its taken the freon to leak out. In a car system, eventually(maybe many many years/decades) freon will seep out past comp seal, orings, etc, without a substantial leak. For the diy a can of freon is cheap way to see how long a charge lasts and give one an idea if they do need to go for a leak search.
If you do find a substantial leak, and don't have a quality leak detector,,,
You can also use a Freon with LEAK DYE to help pinpoint a leak without a freon leak detector. Don't mistake leak dye for a freon with leak stop, 2 very different things. Never use leak stop in any ac.

Take my 996.1 car. When I got it a few years ago with 31,000 miles the ac wasn't blowing cold. Put my gauges on, it was low, under 20psi low side at idle. Dumped not even a full can in and got it to where I liked the pressures and was blowing 45° out of the center vent. Just got in car today low 80's ambient temp here. I keep a digital thermometer in my center vent, it still read 47° after short ride, 3 years after I charged it up. Did notice when I pulled off the gauge hose a slight leak in the low side schrader service port. I always put some soap suds leak detector on service ports after I pull gauges as they seem to be a common slow leak/seep area in all types of ac. Tightened the service port cap down tight, and will have to deal with that eventually, but its been 3 years is my point...

To answer your question...
"Switched off car, but then the gauge started to go into the red up to 80. Freaked out cause I realize i have no idea what this all means."
Normal, don't worry.

As soon as the compressor stops hi & low sides pressure will start to equalize till they meet. Freon is an organic gas, pressure is temperature. A jug of freon normalized in a 70° room will have the same pressure always at that temperature regardless of how much freon is in the jug, 1lb or 25lbs, doesn't matter, temperature is pressure. Same jug of freon in a truck bed in the sun on a 90° day will have a very much higher pressure.

theprf

What allcool said. You were probably about empty on refrigerant. I don't have the manual handy, but I would bet it takes about 1.8 to 2.2 pounds of refrigerant to fill the system. How much does a can hold, should say on the can. I haven't bought cans in years I buy the stuff by the 30 pound jug... I would think you need quite a bit more refrigerant. The amount of refrigerant needed should be on a sticker somewhere near the fill ports.

When to stop filling? Without a high side gauge it's a bit of a guess. The best way to tell is what I mentioned earlier: A/C on max low, fan on high, doors open to put the highest load possible on the A/C. Then add refrigerant a little at a time until the suction pipe at the compressor is cold. When it's cold to the touch and water is condensing on it that's the minimum amount of refrigerant. Add a tiny bit more and call it done.
Do check the fans although I doubt that is the problem. Just turn on the A/C and feel for air exiting under each front fender in front of the wheel. The fans should run on low speed as soon as the A/C is switched on, even if there is no refrigerant in the system at all.

Edited to add, if there is a persistent leak and the system is repeatedly refilled eventually there won't be enough oil in the system. This is because when refrigerant leaks out some oil leaks out too. Eventually there is not enough oil to lube the compressor and it seizes up. This is a super common problem on Chrysler cars from the 90's through 2015 or so as the evaporators always leak, and it's a really big job to change the evaporator, so people just keep refilling the A/C until the compressor self destructs.

Ben8jam

Thank you both for taking time to reply. I did some more reading up online and saw the low side reading high pressure was normal after system turned off.

I will try again tomorrow and see if the compressor pipe gets actually "cold". I found a layman's 134a chart online and 75F ambient should equate to 40-45 PSI low side. I'll try not to stress when turning OFF the car and watching gauge climb. Both radiator fans kick on and blow no problem.

As mentioned, I did feel the "coldest" air in there since I bought the car 17 months ago after that partial can. So fingers crossed it really has just leaked out. I can't make it through another summer with no AC (cab or not!). Car came with 99k miles and I've put 3k on. Just replaced water pump,thermo this past weekend, and judging by that the freon may never have been serviced in who knows how long.

Mike Murphy

My 99 goes from 675 RPM to 800 RPM when I press the AC button. It doesn’t drop.

Ben8jam

Yes typo.

Ben8jam

Further update. I bought another can of 134 with UV dye.

Brought car out into 75F sun. Ran it with 134 and gauge connected. At cold and off it was at 80psi.

I turned on full AC and it dropped to 38PSI. I opened the valve and let the freon flow in while revving engine around 2k. Put a thermometer in the vents: 70F (it was 80F ambient in the car).

When I revved engine, thermo pen temp would raise to 76F.

Here's the odd part now. Gauge is sticking to 38psi, valve is open, can is cold, so freon moving, but going very slow. I suddenly hear the pasenger side radiator fan kick on high. Realizing it was running at all. Drive side is running constantly. (they did indeed run before because i tested them a few months back, but something may have changed, I did just change the water/pump coolant).

When passenger side radiator kicks on on high, the pressure on the low side drops to 25psi. Fan then turns off and psi rises back up.

This happened on and off with car is at operating temp with needle straight up.

Is there something wrong with my fans? They obviously work, but I thought it should have been on all the time when AC on. Also I remember them kicking on when I got home and idled, and now they come on for a brief moment. Even when coolant temp got to 208F (turned car off at that point).

Temp on thermopen did get to 60F. Probably the lowest it's been since I've owned it. I felt the rubber pipes in engine bay. One is very hot, the other is just normal temp.

I removed the 134 as I just get nervous. It still feels very full.

theprf

The radiator fans should run on low speed as soon as the A/C is turned on. When the high side pressure exceeds some value, probably around 180-220 PSI the fan shifts to high speed. That is pretty normal with the car not moving and the A/C under high load. But, both fans should come on the same speed so if the driver's fan was not on high then something is up with the fans. Do check they both work.

There is a pressure switch mounted next to the filler ports in the cowl that does three things:
#1. Disables the compressor (but not the radiator fans) if the A/C system is empty;
#2. Disables the compressor (but not the radiator fans) if the high side pressure is too high (like 450-500 PSI);
#3. Turns the fans on high speed when the high side pressure is moderately high, which forces more air over the condensers, which brings the pressure down, which switches the fans back to low speed, and the cycle repeats.

At this point you really need to figure out the high side pressure. Also I suspect the blend door in your heater box is probably not sealing because the noise deadening foam is long gone so you are getting heat from the heater core mixing with the cold air from the A/C evaporator. That will never work properly, the heater is many times more powerful than the A/C.

When you say the "rubber" pipes, those are the air conditioning pipes? The output from the compressor will always be very hot which is what it is supposed to be. With the other being "normal" you probably are close to the correct amount of refrigerant.

allcool

Something sounds strange in your charging set up...?

Can you take a pic of the setup you're using to charge with..?

Might be time for a cheapy Amazon set of gauges and vac pump. This is not an industrial quality every day professional use type tools, but more than sufficient for the diy guy,
Amazon Look around on Amazon, lot of these type diy kits, make sure to get one good for cars 134

Then you can start from scratch and see hi&low pressure that will help troubleshoot the system. If you do need to change out a leaky component you'll need these.

Ben8jam

Yeh, i'm pretty lost at this point. I had read somewhere the blend doors didn't affect temp that much, but if they do, then this whole process is useless cause mine are likely very shot considering all the foam i've cleaned up over past year.

Here's the gauge, also from Amazon. Didn't know at the time I needed high side too. Most general diy ac docs made it seem like just a can-o-134 solved all.

And of course now I have to diagnosis both fans not turning on with AC and why high speed takes so long (if at all) to kick on. Sigh.

allcool

how many full cans have you put in the system..?

Ben8jam

probably a little over one? had some technical difficulties with thr first one. and second, even though it was on low for a while, still feels pretty full.

im really nervous of over filling

allcool

Our cars take iirr 32 oz r134a. I'd try dumping the rest of that can in and see if your vent temps go down. Not sure what you meant by technical difficulties, assume you're having trouble getting the freon in. Make sure on your set up to fully turn in the needle valve to puncture the can fully, then back it out all the way. Charge at 1500-2000 rpm. Our cars have a long pipe run from the low side service port- to the compressor, so you can dump some liquid in for a few seconds at a time (invert can briefly a few times) might help to get all the dye in and charge faster with a small can...

The foam vent seal problem theprf explained is interesting, never thought of that. Without the compressor * on, but in hi fan/max cooling mode, does heat come out your vents, what temp do you get compared to ambeint..?