Mcsquare23

A/C not cooling and gauge not working after replacing defective outside ac gauge. Gauge was reading -15 in 70 degree weather than would climb to almost correct temp as I drove. It did that for about a week than disconnected the outside gauge to check for problems and noticed nothing strange. When I replaced original gauge it read --- temp. So I ordered a new one and replaced the old thinking that could be the problem. Gauge is still flat lined and ac is not cooling. Throughout the strange temp readings the ac would sometimes cool and sometimes heat while driving so I stopped using it until I replaced the gauge.Have I missed a step? Would really like to fix this before hubby does so I can gloat a little.