Calling all A/C experts - Red Tek filling

[RufusRockwell]

Background - I have an 85 tintop with the roof mounted A/C on the ceiling behind the driver and passenger heads. It works fine for the most part and has all new hoses and components that I re-did when I did a Subaru 2.2 swap. It's running Red Tek.
I'm wondering if it's full enough because while driving, it blows pretty cold. At highway speed it's very cold, but at idle - like when I first start it up and flick on the A/C, it is cool but not cold. I understand that the air over the condenser is a factor but it seems like it could be colder at idle.
There is also an occasional gurgle/slurping sound from the expansion valve that I read could be a sign of low refrigerant.
When I initially filled it, It took 2 cans of Red Tek. I read other threads that 3 cans is what most vanagon systems took.
I ordered 2 cans of Red Tek and figured I'd try to add some. I should point out that I'm always a bit hesitant when working on the A/C because I'm afraid I'm going to overfill and blow something up.
I hooked up the gauge and can, started the motor, and turned the A/C on full. At idle, the gauge indicated "filled" and was right around the blue arrow in the picture. As I had done before, I revved the motor and the gauge went down into the green around the green arrow in the "low" area.
It's hard to tell if the system is taking in anything and rather that keep going, I aborted the mission so as not to overfill the system.
I figured if I get the gauge into the blue area when revving, it might sit in the Alert or Warning area when Idling.
I'm also only reading the low side as I don't have a gauge for the hight side.
Should I try again to add mor Red Tek? I'm really unsure how to proceed.
I know these A/c systems are not quite state-of-the-art but I would like to improve the performace and have it filled properly if possible.

[jlrftype7]

IF, you installed a Receiver-Drier as new into your system when you were rehabbing it, and it has a sight glass on it, you can watch with a flashlight and mirror while the system is running, to get an idea of how filled your system is.
Lots of bubbles passing past the glass, or a big amount of them before they disappear, and the glass goes clear, you're probably a bit low.

Ideally, get yourself a set of actual A/C gauges to measure both Low and High side pressures. When you rev the engine, and spin the compressor faster, you may see the Low side dip a small amount, but until you have a more accurate set of gauges on the vehicle, I can't say how much I'd trust that gauge that came with the Red Tek. Even for just checking the Low Side....
Steady idle speed, and depending on ambient temps, you might see a steady 40 psi or a bit lower with the Compressor Clutch engaged. You don't want to go below 32 psi since you're getting into Evaporator Freezing territory there.

R-134 would read higher due to its different chemistry, esp High Side readings.
Even with Red Tek, you'd really like to know both pressure readings, and with any luck, you have that sight glass on the Receiver-Drier.

You can also put a fan in front of your Radiator/Cond to see if a steady amount of air across those two parts gets you a cooler interior output at idle.
You should be running at least a low speed on the Radiator Cooling fan once the A/C is running. That's how our '84 is wired with the same system you have. Low Speed always on with the A/C on.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[mrinnovation1]

I'm no expert as I don't know a lot about AC systems but I've always understood that you can't overcharge the system if you are strictly "drawing" the refrigerant into the system as opposed to "injecting" the refrigerant into the system. When drawing refrigerant, it won't take anymore when full. I've always added refrigerant by drawing. Someone correct me if I'm wrong on this!

[khughes]

You can certainly overfill them. The compressor is a pump, plain and simple, it doesn't "know" when the "right" amount of refrigerant is in the system. As long as you keep pressure on the suction side, the discharge pressure keeps going up. You can charge the system at 70F just looking at the low side, and put enough refrigerant in the system to blow the high side hoses as soon as it gets to 100F ambient. You'll likely be flooding the evaporator with liquid refrigerant before that and losing your ability to cool, or get liquid refrigerant out of the evap and back to the compressor, where bad things ensue, but you can certainly do it. You *always* need to monitor both suction and discharge pressures, otherwise it's a crap shoot.
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'86 Westy FAS GenV Turbo (Marvin)

[SLOWoody]

Was a vacuum pulled on the system before it was filled with RedTek? I don't see that this was mentioned by the OP. If the system was opened for any reason (hoses replaced), the air needs to be vacuumed out of it before any refrigerant is added back in.
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83.5 Westfalia, GW 2.3L w/ GW EFI, 4 speed

[MarkWard]

You should be checking high and low pressure at 2000 rpm. The low side is actually an indication of evaporator core temp. Lower pressure is actually proper at rev. Adding too much Freon has the opposite effect.

It sounds like your system is responding accurately. I’m not sure how you have your radiator fan configured. My fan is on low when the compressor is engaged. There is a pressure switch that runs the fan on medium. High speed is for only coolant temp.

Depending on sunlight and outside temp, it’s not unusual in Florida to have less cooling from the AC at idle. This is for many vehicles. You can purchase real AC manifold gauges from the big A for cheap. I have no experience with Red Tek. It’s not practical for shops without a way to recover it. We’ve had good luck with R134 being retrofitted in R12 systems. You run less refrigerant with 134 and it can be recovered most places and recycled. You don’t use the sight glass, you charge using pressure only.

[RufusRockwell]

[Howesight]

Since the AC system provides good cooling when the engine is run at highway speed and the vehicle is moving at highway speeds, I do not think that anything is wrong with the OP's AC system per se.

It is possible that adding some Red Tek will help, but guessing is not an option. A proper set of AC pressure gauges is required together with an AC vent temperature thermometer if there is any concern about the fill level.

You can Google Red-Tek's conversion charts that show the recommended weight (NOT volume) of Red-Tek to install if you have the factory-recommended weight of R-12 refrigerant.

However, I suspect that this is all beside the point. The most likely problem that I see in the info that the OP has provided is no problem at all - - the 1984 Vanagon had a weak radiator fan, a poorly-executed condenser, and far too many air leaks around the condenser. At idle speed, all you have is the cooling that the measly amount of air pulled by the slow rad fan through the condenser can supply. On the highway, the air flow through the condenser is massively increased, which is why the evaporator cabinet cooling output is far better.

I improved the idle and low-speed performance of my home-built AC system significantly by blocking off all the passages through which cooling air could by-pass the condenser.

For the OP, here is what I would recommend:

1. Adjust the idle-up engine speed to increase idle speed when the AC is switched on.

2. Install foam-rubber all around the perimeter of the condenser so that the radiator fan can do its job better. When sealed in this way, the rad fan pulls more cooling air through the condenser instead of sucking the air through the gap between the condenser and the radiator;

3. The Syncro Vanagons and all 1986+ Vanagons with factory AC used a 450 watt rad fan. The earlier rad fans were, by comparison, wimpy.

4. If the above hacks don't yield enough cooling improvement, then install a parallel-flow condenser like the 16" by 24" one offered by Nostalgic Air and other vendors.

Here's mine (before installing the sealing foam rubber around the perimeter of the condenser):

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'86 Syncro Westy SVX

[RufusRockwell]

[MarkWard]

High pressure, I’d be expecting somewhere between 200 low to 275 psi high. At 300 it’s getting to high. The high pressure side actually better reflects a low charge. It has a wider working range.

[dhaavers]

[jlrftype7]