I have a Heil gas furnace. It is a high efficiency type built in 1983. When I went to change the thermostat from cool (summer mode) to heat (winter mode) the furnace came on but only blew cold air. I went to the unit and pulled the cover panel off. I saw that there was no combustion flame. The combustion air blower was on but no flame. To trouble shoot, I replaced the furnace filter, checked the discharge pipe to make sure it was not plugged, and then pulled the vacuum line off the combustion air blower. I slightly sucked on tube going to the vacuum switch and the pilot ignited and gas came on with full flame. As soon as I sopped applying suchion to the vacuum switch the flame went out.
Does this mean I have a bad vacuum switch or could it be something else. I even sucked on the line, got flame pinched the line and the unit ran through a complete cycle until the upper heat exchanger sensor told it to shut down flame.

The chances of a bad switch are slim indeed. That switch is a safety device to prevent firing if there is no draft. When you switched to heat, did the combustion blower come on? If it did, take a paper cliip or something similar & push through the nipple where the hose connects. Clogging in a common problem.

I did that to no avail. Just don't know what could be causing this issue. When I switched from cool to heat the combustion blower came on and the unit just pushed cold air when the main blower came on. That is when I went to check it out and tried sucking on the vacuum switch which ignited the burner as it should. I then put a paper clip in the orface of the fan where hose attaches and felt some resistance but it went through. Then reconected the hose and still the burner would not fire. I just don't want to go out and buy a combustion air blower or vacuum switch if that is not the problem.

So much for the most common problem.
Next, I suggest you take the vent system apart & check for blockages. One thing to particularly look for is any sag in the vent system which could trap water.
You could disconnect the vent at the furnace & try for ignition. DO NOT ALLOW THE BURNER TO RUN MORE THAN A VERY FEW SECONDS.