HELP: Troubleshooting an old upright manual defrost freezer


Hi all. Am hoping I could get some help in troubleshooting an old freezer.
Make: Admiral Model: F1073, upright manual defrost Year: early 1980s
Problem: Excessive frost buildup requiring weekly defrost
http://i17.photobucket.com/albums/b65/emote623/freezer_make.jpg
Freezer make.
http://i17.photobucket.com/albums/b65/emote623/Freezer_ceiling_n_top_shelf.jpg
http://i17.photobucket.com/albums/b65/emote623/Freezer_process_tube1.jpg
http://i17.photobucket.com/albums/b65/emote623/Freezer_process_tube2.jpg
Main areas of frost build-up are at the ceiling and the underside of the top shelf, along with the process tube (tube1 is the segment beneath the top shelf, tube2 is the segment beneath the middle shelf).
http://i17.photobucket.com/albums/b65/emote623/Freezer_top-n-middle_shelves.jpg
Note that there is no frost buildup under the middle (or the bottom) shelf.
I have no experience in appliance repair, but am a technical sort, and have a multimeter handy. Have borrowed a bunch of books from the library on appliance repair, but none give any specific steps on troubleshooting a freezer with excessive frost buildup. But they do give some general guide on things to look for.
Steps taken:
. Put a thermometer (in cup of veggie oil) in freezer to measure temp. Temp seems to be at -10 to -15 degree F, which according to the books is probably too cold (they cite a range of -10 to 10 degree F). The temperature control knob is already set at the minimum setting without shutting it off (there is a click before getting to the off position, and the motor does turn off when I turn the knob to the off position).
. Visual inspection of the surrounding seals seems OK, other than this spot
http://i17.photobucket.com/albums/b65/emote623/freezer_seal.jpg
I tried that particular spot with the dollar bill test (i.e. put a dollar bill in between and see if it can slide in/out easily), and the seal seems to hold up.
Some books talk about a thermostat, but apparently that's only for auto-defrost models. One book does show a thermostat element for manual models that's underneath one of the shelves, but I didn't find anything like that. My assumption is that this manual model doesn't have one.
My next step is to pull the temp control housing and check for resistance at the highest (little to no resistance) and lowest (high resistance) setting. My hope is that it is the culprit, and I can just replace this item.
The books also recommend cleaning out the condenser coil (at the back of the freezer, not the bottom). I don't see any excessive dust build-up on it, however.
Aside from the temp control, and more thorough checking of the seals, I'm not sure what other areas to try for this particular issue. I hope that someone here can provide more advice for me. Thank you in advance.
HP
http://i17.photobucket.com/albums/b65/emote623/freezer_make.jpg Freezer make.
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Hi, this is a correction of my original post, to fix some broken links to the pictures posted. Please reference this post instead. Thanks.
HP
bipster@comcast_diespam_.net wrote:

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