P-h diagram question

[apford]

Hoping someone can help me with understanding this - 

The problem involved an ammonia (R-717) system description. High temp is 120F, low temp is 20F. The problem asks for the work done by the compressor and references a P-h diagram for ammonia. I understand that the work per unit mass is the change in enthalpy between the two points (low temp at the 'dry' side of the saturation curve and the high point in the superheat region where s1 = s2). My method was to find entropy at the first state, then follow the entropy line into the superheat region until it crosses the high temp line. 

The solution for the problem in the back of the book takes the horizontal line for the high temperature in the saturated region and extends it straight out into the superheated region, and then reads off where that line and the entropy line intersect. The problem with this is that the temperature as I read it at this point is ~265F, not 120F. 

Am I misunderstanding something? Sorry for the poor explanation of the problem.  

 

[apford]

Nevermind - I think I get it now.

I was misunderstanding "operating between the temperature limits of 120F condensing and 20F evaporation" as limiting the maximum temperature at 120F where in reality it means the high pressure is the saturation pressure at 120F, which you then extend out along a constant pressure line into the superheat section to find enthalpy.