For
sake guys, the original Troll post asked about the
cold air unit!!!!
He is not asking about engine compressors.
Methinks you lot of experts now need to research cold air units. Try Goggling Bootstrap systems.
(btw, I lecture this at professional level....)
Alternatively, ignore the Troll and do something useful. 
Stall (rotating stall more accurately) is a flow breakdown at one or more rotating compressor blades. Typically, a rotating stall is a stagnated region of air which moves in a circumferential direction of rotor rotation, but a fraction of rotor speed. At a given throttle setting it does not move axially in either direction, although it may cause pressure waves to move upstream (compression waves) or down stream (rarefaction waves).
Surge is a response of the entire engine which is characterized by flow stoppage or reversal in the compression system. Upon surge, a compression component will unload by permitting the compressed fluid in downstream stages to expand in the upstream direction, forming a more or less planar wave which at high speeds leads to flow reversal. The compressor can recover and begin again to pump flow. However, if the surge inducing cause is not removed, the compressor will surge again and will continue the surge/recovery cycle until some relief is provided. Surge may be initiated by a rotating stall.
There are two types of stall one can distinguish. Blade (rotating compressor component) stall is a two-dimensional type of stall, where a significant portion of the blade airfoil has large wakes due to substantial thickening or separation of the suction surface (convex surface, i.e., up-side of an aircraft wing) boundary layer. Wall stall is an end-wall boundary layer separation (airfoil tip area).
Stall margin is a measure of the operating range between the design point and the in-stall point. Typical design values of stall margin range from 15 to 25%. For each compressor design, a compressor performance map can be drawn to assure there is an adequate stall margin built in for the total engine operating envelope.
Mass Flow...
As mass flow is decreased (throttle closed), pressure increases and the compressor will operate along the unstalled operating line. Further reduction in mass flow will bring about rotating stall. If the mass flow is increased (throttle opened), the compressor does not jump back to original point on the operating line but along a stalled characteristic line until such time additional mass flow causes it to revert to the unstalled operating line.
Hope this answers your questions regarding stalls, surge and mass flow.
I can lecture this in 50 minutes IN ENGLISH!