To add to what Bruce said (I was taking pictures when he posted):
To take the top off of the Penguin, it's 4 screws, two in the front and one on each side toward the rear. After that you'll be able to get to the control board (which is behind a metal cover on the passenger side) and the ambient temp sensor.
Here's a pic of the area, I've already taken the top off the control box, that's where all the wires are:
Here's a pic of the sensor, it's the black wire going to the yellow ring terminal on the left of the control box:
It has a red 2 pin connector on the board side.
is the service manual, the ambient sensor is described on p33 (p35 of the pdf). The last page of this
installation manual shows the ambient sensor connected to P3 on the board, that is the red 2 pin connector. When you remove the sensor you can use a DMM to determine if the resistance is good using the chart on p33 of the service manual. It would be a good idea to determine this first as the issue could also be with the control board. BTW, you can "fake" a temperature by connecting a resistor close to a value that is on the chart to the two terminals on the board just to see if it fixes the issue.
Regarding replacement parts, PM me if you need them and want some used ones, I have two 630515's in the basement and can get the parts off them and send them to you, no charge. The controls on both worked when I removed them, the compressor failed on one and one of the capillary tubes sprung a leak on the second. It wasn't worth fixing them but I never threw them away. I am on the east coast so it will take about a week to get there.