Like Cravin says, it can catch fire. The Intermatic mechanical timers are rated for 15 amps max - not "2x15 amps". A 400 watt HID pulls about 4 amps at 110 volt. Look on your AC and see what it says it draws for amps. You never want to try and use the full amp rating of an electrical outlet, aim for about 80% or about/around 12 amps.
Those mechanical timers are a real risk point for safety. If in doubt get a second timer for the AC, and put the timers on a power strip which has a fuse or circuit breaker built-in.
400+400+ac unit watts= total watts is that over the limit? It is not good to constantly push electrical components to the max amp/wattage it will lead to early failure as more juice equals more heat going thru them. If you can get that ac on a different line you would do well. Remember that you also do not want to overload the breaker in the powerbox.
All amps are not created equal. Your timer is rated for 15a, but probably for a resistive load, which would be like a heater. Depending on what type of ballast you are using, the load is either capacitive or inductive. These types of loads normally de-rate the timer contacts down to around 40%-50% of the resistive rating. The full contact ratings are probably not listed on the timer, you would need to take the model number and research the full specifications at the manufacturer's web site.
Try using a florescent light below...if the rating won't take it....or take the ac off of it and use the temp setting and just let it run 24/7 in it's own plug...ac on timer is a bad idea...might burn the house down and no one wants that believe me! Real bad scene plus the cops called on your grow....smoke ruins everything in the house...
Mine just wouldn't work with too much shit plugged into it. At first I was thinking you'd be good with that big wattage rating, but on second thought that amperage might heat it up, that could be dangerous. Maybe get another one to plug some stuff in?
BTW, just curious, I thought you had to pick/harvest before 1Feb. Wuh hoppen wif dat?
I have seen some burnt up timers, not mine but others. They look scary, scary enough I won't use the cheapys anymore for anything pulling any kind of amperage. What happens? Well the fire department can show up thats for sure.
Sweets .... if you are hell bent on using the cheap timers .... get one for each device . 1 for each light & 1 for the AC . i've seen them damn near melt with just an AC plugged into it .
my suggestion would be look into the Intermatic 101 & hook a Quad receptical to that .
running a grows AC or vent fan on the same timer as the main lighting is a sure way to have problems with PM or mold
a better solution would be to run the AC on its own thermostat and the two 400's on the timer