Problem with ADC12 single conversion - repeated

I've written a function to perform a single conversion using the ADC12. I pass the channel that I want to convert into the function (for example, analog input A3). The function works the first time I call it, but I get inconsistent and wrong results on subsequent calls to the function. I've read through the users guide and do not see anything wrong with my code. Can someone please take a look at the code below? Thanks.

int ADCread(int Channel)

{                                

  ADC12CTL0 |= ADC12ON;                               // ADC12 core on

  ADC12CTL0 &= ~ADC12ENC;                         // Disable conversion

  ADC12CTL1 |= ADC12SHP;                             // Use sample timer

  ADC12CTL0 |= ADC12SHT02 + ADC12SHT01 + ADC12SHT00;           // sample time = 192 clocks

  ADC12MCTL0 |= ADC12SREF2;                       // select external reference

  ADC12MCTL0 |= Channel;                                 // select input channel

  ADC12CTL0 |= ADC12ENC + ADC12SC;          // enable and start conversion

  while (ADC12CTL1 & ADC12BUSY);                 // Wait for conversion to complete

  ADC12CTL0 &= ~ADC12ON;                             // ADC12 core off

  return ADC12MEM0;                                          // Return conversion result

}