One thing you may want to try is to switch the TX and RX. It’s often confusing whether the TX pin on the serial converter should be connected to the TXD or RXD on the microcontroller.
I have not had any experience using Max232. I’ve been using the PL2383 USB-to-serial converter for debugging with OpenSprinkler and it works pretty well. We have this in store:
To use it you just need to plug in the ground (black) wire to OS ground, and the RX (white) wire to OS TXD pin. Then use a serial monitor (either Arduino’s serial monitor, or putty, or gtkterms etc.) to receive messages. The only downside with pl2303 is that on Windows you need to install driver.