What does this AC symbol refer to?
More than likely they are varistors. Varistors are bi-directional voltage clamping devices also known as MOVs (metal oxide varistors). They sit generically under the umbrella of TVS devices where TVS stands for transient voltage suppressor.
In your circuit they are located under the heading &quot;surge absorber&quot; because that is what they do. They are used for indirect lightning surge suppression. Here's a general symbol picture of surge protection devices: -

Although your circuit is NOT showing them as the top right symbol for an MOV, it is quite likely that they are given they have an identity of VA001 to VA003. Engineers can be lazy and use the wrong symbol but, a surge doesn't care about the symbol only the ability of the device to cope with it.
It's quite possible that the devices look rather like these: -

The reason they are not thyristor TVS devices (bottom left in symbol table) even though they have a much closer symbol resemblance is because triacs are not usually suitable for this type of application - they tend to be more of a final resort and might blow the fuse if activated because they will clamp down to a couple of volts and this also clamps the regular AC supply causing potentially hundreds of amps to flow in a half cycle.