2001 Blazer A/C cold is off and on

I have a 2001 Blazer. This summer I noticed the A/C will be okay for a while, then it begins to blow air like I only have the vent on. I can be driving 60 MPH when it happens. It doesn't happen only while stopped in traffic. The ENG TEMP is still in normal range. I have added refrigerant, but it doesn't seem to make any difference. I don't know if I have a leak, but then would it work off and on if refrigerant was low? I suppose the compressor could be cutting off, I haven't checked that yet.

did you use a gauge when you refilled the system?

did you use a gauge when you refilled the system?
No, I didn't use a guage. I should go buy a set and see what reading I get.

No, I didn't use a guage. I should go buy a set and see what reading I get.

Yes, never blindly add refrigerant without knowing how much you have in your system.

Also check the pressure with the AC and fan on max for a proper reading.

Yes, never blindly add refrigerant without knowing how much you have in your system.

Also check the pressure with the AC and fan on max for a proper reading.

Thank you for the advise. I was driving home from work this afternoon. I was driving down the highway at 60 mph. A/C was working fine. Then, it started blowing air like I only had on the vent. I left it alone and a few minutes later the cold air came back on. Makes me also wonder if my compressor is not working at times. Will being low on gas do that? But no more than guages cost, it will be worth the investment. Thanks again.

No, your compressor is nor turning on due to lack of refrigerant.

It won't turn on until there is enough pressure to kick the pressure switch on so the compressor will work.

Also can blow warm if there is too much refrigerant (sic) and it freezes up too quickly... It will stop to thaw before it restarts again.