I was supposed to get a refund of $2438. I only got back 1600... how do I find out where the hell the rest of it went?

Are you also supposed to get a state refund?  If so, they come separately at different times.  If you're supposed to be getting both refunds, don't go by the total refund amount that TurboTax displays at the Tax Home that shows the 2 refunds combined.   For your Federal refund amount, look at what is on your Federal Form 1040, Line 21a.   Then subtract any fees if you chose to pay out of your Federal refund (plus the $40-45 service fee and sales tax.)

If an as-yet-unreceived state refund doesn't explain it, and if the IRS reduced your refund, the IRS will send you a letter in 3 weeks or so explaining why, although with the marked slowdown due to Coronavirus I don't know how well they are staying on track with communications.    Normally you'd be able to phone them to ask about it, but they are all but closed, but if you want to try, we can tell you how to try to reach a live IRS agent.

You can also check the IRS "Where's My Refund" tool.  If there was an offset applied by the IRS to your Federal refund due to a debt, you may have word of it at the WMR tool.

https://www.irs.gov/Refunds

NOTE:  That IRS tool is down for maintenance during the night every early Monday morning and likely will not find your information until later today.