Greetings in need of advice
 

I have an 98 audi a4 1.8t that is over heating I'm sure its because the cooling fan won't kick over to high speed to cool the engine it only spins according to rpm I have replaced thermostat and coolant temp sensor this is my daily driver so if u guys have any tips plz let me know both of the fans come on when a/c is on but still dosnt cool engine

Are you sure you got all the air out of the coolant system? I'm not sure of the particulars on how to bleed your A4 but there should be some bleeder points around the high points fo the coolant system. Usually on top of the heater hoses where they pass through the firewall to the heater core. Here's a video that might help. The kid shows you how to bleed it near the end of the video.

I'm not sure but I did replace coolant thermostat and coolent temp sensor checked fuse the 5 amp is fine and the 40 amps are replaced relay 213 and 214 are good it runs until it overheats cause the fan won't kick Into that second faster speed

You need to make sure you get all the air out. The temp sensors cannot accurately read the temp of hot air. There has to be direct contact with the coolant. Also, I'm showing two temp sensors for these cars. One for the ECU and Temp gauge on the dash and another (looks just like the one on my 944) that goes into the radiator that controls the fans. 98 1998 Audi A4 Quattro Cooling Fan Switch - Cooling System - Beck Arnley, Four Seasons - PartsGeek

How can I test this coolant fan switch be for I buy another ?

I hooked the car up to to try to find codes but it says it's the coolent temp sensor witch I have already changed out.

As cheap as the sensor is, I'd buy another and put it in. You'll probably have to drain and rebleed the system. You could test it but the time it would take to test it, you could have already replaced it and been done.