My thermostat will trip my heater to turn on. The inside blower turns on but the outside unit doesn't turn on. I can get it to go by turnign off the unit at the thermostat and waiting a minute. I turn it on and off until I hear the outside unit turn on. The problem is when the Thermostat turns if off after it hits the right temp it doesn't come back on when it gets too cold and the thermostat turns the unit on. The inside will go but the outside won't. So, it gets colder and colder in my home until I turn if off. I have a gas heater/ac unit. Its an old one and is all in one. It is gas with a pilot light which is lit. Its just the outside unit won't always come on so I have to play with it until it does. Does anyone know what this could be from? I have a feeling it might be loose wiring but am not sure. Please help!

If your unit is as old as you say The contacts are probably not sealed from the elements, When the unit is off, bugs may have gotten between the contact points, When that happens
It's fried bugs. Now when it closes the fried bugs keep the points from contacting properly. Or else the points are so pitted or corroded the points do not make good contact.
I would say you need a new relay. . Jocko009