My freezer has been warming up off and on for a week now, when it warms, the ice melts and food is not frozen, but the fridge is working fine. Now after a week of off and on, the freezer is not cool enough to freeze the water in the ice maker. The fridge is still working fine. Where should I start to troubleshoot?

Frigidaire FRS26H5ASB5

Here are your parts
Parts for Frigidaire FRS26H5ASB5 Refrigerator - AppliancePartsPros.com

Here is the tech sheet
http://manuals.frigidaire.com/p...f/Anderson/240389608.pdf

I am going to assume that the compressor and it's fan run all the time other than when the unit goes through a defrost cycle.
Also that the evaporator/freezer fan is running.
If not then the below may not apply.

First remove the evaporator cover in the freezer so you can see the coils.
If they are heavily iced/frosted over then it is a defrost problem.
Do not let them de-ice.

If yes.
Manually force a defrost cycle, see the tech sheet. When the fans and compressor turn off, you are in defrost.

Now check the defrost heater (item 14 in section 13) to see if it is on.
Be careful you do not want to burn your fingers.
If the heater is on then the adaptive defrost board (item 23 in section 11) needs replacing, re: it is not automatically programming a defrost cycle.

If not on.
Unplug the unit.
Remove the wire for one side of the heating element (Item 14 in Section 13) from the wiring and measure it for continuity, should be around 30 ohms or so.

If the heater is OK
Remove one wire to the defrost thermostat (Item 21 in Section 13) and measure it, should be 0 ohms when frozen. Note that it opens just above freezing so must be frozen to check it. Also inspect it, if it is bulged at all replace it even if it measures OK.

If both the above are OK then odds are the defrost board is toast.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.
4. When you start always short the meter leads together. This will tell you that the meter is working and if there is any 0 offset.

There is a good STICKY at the start of this forum about it's use.