Thanks all for the advice and links!

Quote from: JCA433 on Today at 02:19:30 PM

This is the fan I use.  Seal the gaps around the fan.

https://www.amazon.com/gp/product/B07VWLSMN1/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1th

I didn't seal anything

Granted, my fan is 60CFM, but I didn't seal it. Still sucks hard enough to hold an envelope easily.

I wonder if it continues the practicality of collocating a Davis sensor or other sensor of known accuracy in the MMTS shield? Any insight on who manufactures that shield? I’ve searched in vain.

Same here, I couldn't find anything on the shield maker, wonder if it wasn't just a one time outside contract due to the fact parts are scarce. I was told this on installation they have to reuse connectors because they are no longer made.

Provided the Nimbus sensor is correct. It's running cooler than the SHT-31 FARS by as much as 2° once we reached into the low 90s one day.  Guess the best way to know for sure would be to open the shield and insert a SHT-31 inside and see how it compares with the nimbus probe.  I did read somewhere when they started replacing the CRS with the MMTS they noticed about a degree cooler on the MMTS. 
I can say the airport ASOS is right with the FARS SHT-31 most days for highs. While the MMTS will lag back a bit on some days. 

This is the fan I use.  Seal the gaps around the fan.

https://www.amazon.com/gp/product/B07VWLSMN1/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1th

Yet another Davis fan has quit and they are now over $100 including shipping. 

LOL! You gotta be kidding me?! Tell me everything is fine.  Must be sold at the grocery store.   Unbelievable.

Here's what I use. Overkill, but works in my climate just fine. i'd shoot for the 25-45 CFM range. Don't go lees than stock.

https://www.coolerguys.com/collections/dc-12-volt-fans/products/sunon-80x25mm-high-speed-12v-fan-with-3-wire-3-pin-connector-pf80251-000u-g99

Is there a difference in the old sensors, and the new sensors?  I believe I saw something about a humidity correcting needing to be applied.  My replacement sensor should be here in a week or so.