UART communication with NDIR HC SJH-5 (methane gas sensor)

void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
}
void loop() {
// put your main code here, to run repeatedly:
if(Serial.available()== 1)
{
Serial.println(Serial.read());
}
}

I am apply above code and send the command as given in the data sheet, but result will show randomly .
please help me to short out this problem.