This chart shows the expected pressures at given temperatures.
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Relay voltage should roughly be battery (+) voltage with the engine running and A/C on.
If it is cooling OK while you are driving, but blowing warm when you are stopped at an idle, then it doesn't sound to me like a TIPM or relay problem.
Do the radiator electric fans come on and run when the A/C is on and the vehicle parked? If air isn't moving through the condenser in front of the radiator, then it won't blow cold air in the vehicle. Heat needs to be removed from the condenser by the fans running or air blowing through the grille at highway speeds.
While you are driving, plenty of air is blowing through the condenser and it is able to cool the interior.
If the electric fans are not running, then the hi-side pressure will skyrocket and you may have already lost some of the charge out the hi-pressure relief valve. You will need to add charge after the fans are fixed.
At 98°F, I would expect a hi-side pressure of 280-300 psi with the fans on according to the above chart.