Do I program only control channels or all there frequencies? I tried before but it didn't seem to pick up signal when scanning.
I wonder if you understand how trunking works - for a complete explanation, please read the article in the Wiki.
Systems may have multiple sites. Each site will have a set of frequencies. For a Motorola system, there will be between 5 and 25 frequencies. Up to 4 of those frequencies will be identified as possible control channel frequencies. Typically 2 frequencies are identified as primary control channels and 2 are identifed as secondary.
What I do is always program in ALL frequencies for a site I want to monitor. If I just MANUALLY step through them, I might hear pieces of conversations and I should hear the control channel buzzing away. If you don't hear the control channel, that's the problem. If your scanner can not receive the control channel data well enough to decode it, it will not trunk track a trunked system.
One system I monitor has 24 frequencies for one site. 4 of them can be control channels. I have them ALL programmed to MOT, but I lock out the 20 channels not identified as potential control channels. I do this because it will make the scanner work a little less and scan a little faster. Plus if they ever use one of those channels for a control channel, all I have to do is unlock it.
Now having said all of that, one of my scanners, the PRO-92, REQUIRES that all 24 frequencies (in my case) be programmed and unlocked. It is NOT a "control channel only" scanner. So a 2nd problem you might have is that, depending on your scanner, you don't have all the frequencies programmed.
While at it I'll mention again that all of the above applies to Motorola systems. EDACS and LTR have their own requirements.