Using standard manifold gauge set rental from Autozone, I cannot add freon. Low side pressure is around 20 psi when compressor turning. Started with the small can of PAG oil mixed with R-134. Verified can tap is open, both low side valves open, high side valves closed. Bled air from yellow line, so I know I have freon at least to the gauge set. Can will not empty, no freon flow visible in sight glass of gauge set.

 

There's probably a Shrader valve either not getting depressed or there's an adapter missing.

 

I was thinking that too, but the low side gauge shows pressure, so there is flow in the blue line

 

That is incorrect. That does NOT reflect flow, it only reflects pressure.

First, if there is ANY refrigerant (Freon hasn't been used for over 20 years) in the system, both gauges will register the system's static pressure which, for a very rough estimate, is about 1.0 to 1.1 times the ambient temperature in degrees F.

What you have to look for when the compressor engages is the creation of a DIFFERENTIAL between the low and high sides. If the compressor is functioning, the "low" side gets lower and the "high" side gets higher.

Now, when the low side port of the manifold is connected to the supply container and the container's valve is opened, the manifold gauge will show the supply container's static pressure. When the compressor engages AND the manifold's low side valve is open, if refrigerant flows, the low side gauge will drop and, as the refrigerant is drawn in, the high side will gradually rise, assuming that everything is functioning normally.

 

I think I may have the answer, will try when the rain stops. Apparently there are two types of cans for the 134a. The can tap I bought is the older style that has a piercer. I placed it on a can that is meant for the newer style hose. I may have ruined the can with the piercer. They make an adapter so that the piercer valve will fit on the new cans, so I bought that and a new can of 134. So it looks like the lesson is make sure the hose and tap are correct for the can. The piercer is made for cans that are sealed metal at the top. If there is what looks like an aerosol can top you need the other style of can tap. The newer style also says right on the can "Requires self sealing recharge hose".

 

Interesting.

I get my 134a from a friend who does HVAC... a whole tank of it.

Makes me nervous every time I turn the valve on though... don't want it going into the atmosphere...

 

I buy mine at Sams club for about $4/can in a box of 12 or more. You might want to put some soap on the valve outlet of the 30lb can just to make sure it's not leaking.