What will happen if you apply a AC Signal to a Programmable DC load(63600)?
More than likely this programmable DC load has reverse polarity protection. In other words it will only conduct current in one direction. This is easy to check by setting up a low current test situation. Set the load for 100 Ohms or 100 milliamp, depending on the control setting capabilities of the programmable load. Connect a 10 VDC power supply to it in reverse polarity. Measure the resulting current, either with a series ammeter or the built-in ammeter of the 10 volt bench supply. If the current is not 100 mA, but much lower, the load will not conduct from a reverse polarity source. 

This being the case, connecting an AC source to the programmable load will likely result in effectively half-wave rectifying the AC supply voltage. 

If the programmable load shows conduction in the 100 mA test described above, proceed cautiously as there may be some kind of reverse polarity current shunt incorporated in the load resulting in very high current flow during the reverse phase of  the AC input. This could be damaging to the programmable load.

Another way to evaluate the situation is to connect a low voltage AC source to the load and monitor the current flow with an AC current probe and O-scope. As you decrease the load and raise the AC voltage slowly look for asymmetry in the current waveform. If the resulting current waveform is symmetrical, you should have no problem using the load with an AC voltage source.