AC problem

I have a 2001 chevy silverado 1500 HD. Last summer I replaced my ac compressor and dryer after confirming with dye that the compressor was the problem. I just got it running again due a ground wire being broken for the starter relay. I now find that the ac isn't as cold as it should be. I put my gages on and low side is at 20 and the high side is also 20. What could possibly be the issue. Istarted the truck and I didn't see the ac compressor engage.

It sounds like you, still, have a leak. 20 psi is not enough pressure to close the low pressure cycling switch. The compressor will not run until the Low Pressure Switch closes.

From Service Info:  A properly operating switch should open between 138-172 kPa (20-25 psi) and close between 275-317 kPa (40-46 psi).

 

But what does those pressure indicate? A leak in the system? A blockage?

It sounds like you, still, have a leak. 20 psi is not enough pressure

I agree with Chad, definitely still leaking.

Silverado wrote:

But what does those pressure indicate? A leak in the system? A blockage?
 

The pressures indicate that there is not enough refrigerant in the system to activate the compressor.

I took a spray with liquid dish soap and water and turned the engine on and off and didn't find any leaks. I had a can of R-134a artic freeze so I added some to the low side wit the engine running. That activated the pressure switch and I filmed a video hoping I could add it to this message. The low side is at 30 but the High side didn't budge from 20. So I don't think I have a leak. So what do you think those pressure are? Do you think I will need to go and get the R-134a out and then take thing apart

Those pressures are far too low. The high side probably didn't change because they system is still virtually empty.
Typically, if the system is full, the low side pressure will be very close the outside temperature.
If it worked last year (or at least, if it was properly filled with the correct charge, not just an many rinky dink cans as I can afford from Walmart) and the now this year the low side gauge is reading 20 psi static, then you definitely have a leak.
You're not going to find it with soapy water and an empty system. I leak test systems with100psi of shop air.