Do you have an FSM?
I believe the FSM states that the engine is supposed to be at operating temp prior to the compression test. If not, your numbers will be drastically lower than spec.
It SHOULD still show a drastic change from cylinder to cylinder if there is indeed an issue.
Typically, the HG's fail on #6, #1, or between #5 and 6.
If you have a cracked head, the compression test may not catch it unless the engine is at operating temp.
At the very least, you need a way to rapidly turn over the engine with the spark plugs in it. The proper way is to do one cylinder at a time, removing the plug on ONLY the cylinder you are doing. If you remove ALL the plugs and crank it withe the compression tester on only one cylinder, then it cranks too rapidly and gives false high readings.
Make sure the coil wire is unhooked so you don't end up with fuel igniting where it shouldn't be. Don't need any of the belts to do this test if you're doing it cold.
The comment about cold weather is because we've had folks see the steam coming out the exhaust when it got cold and they thought they blew a HG. They are the same people that remove the oil fill cap on the top of the engine, see some milky substance and think the blew a HG, when in fact all that shows is condensation from sitting overnight.
