No. the pressure are different, r22 runs at a fairly low pressure and you shouldn't be worried about blowing your gauges, but you won't be able to determine your super-heat or sub-cooling. for a about $100cdn you can buy the right gauges.
No.
No
Is r-22 Freon compatible with r-134a freon?
Not unless you like the idea of destroying your AC system.
Your AC won't work any better than it did before. Two very different refrigerants, which will not blend, with different superheat points and system pressures. Not to mention that R22 won't carry PAG oil through the system as effectively as 134a, meaning you could end up starving your compressor of lubricating oil, thus burning it out.
134A 134A 134A
Could be you are low of R-134a. You can check the PSI level on the lowside with a gauge and if you are you can add R-134a. Any automotive store and some discount stores will have R-134a and gauges. Also you can check out the videos on the link below with show how to add R-134a to you car, and where to find the lowside port.
There is two types. One is for R-22 and the other is for R-134A or R-410A. You must perform superheat and subcool, measure ambient temperature and wet bulb.
R-134A
No, R22 is for refrigerators and home AC. It runs at a different pressure and you can't use one for the other.
How many onces for 134A refrigerant does GMC Sierra use?