The OP indicated that he has a WFCO 8930 power center. I'm not sure what he actually has, but there is no 8930 (by that name) He may have an 8900 series "30" amp power center with a 55 amp converter installed in it. ????? That's just a guess.... Here's what WFCO has on the market:
http://wfcoelectronics.com/product-c...f-8900-series/
Anyway, WFCO does not have a "lead-acid/AGM" selector switch.
This is from the WFCO website FAQ:
Should my fan run all the time?
No. The fan is controlled by the load. The fan will start running at a low speed when you have approx. 3.0 to 6.0 DC Amp draw. It will increase in speed as you add more load until you have approx 14.0 to 15.0 Amps draw. At this point, the fan is at its maximum speed and will stay there even if you add more load, Should amperage drop below 3.0 to 6.0 DC amps, the fan will shut off.
Can I use AGM or Gel batteries?
AGM batteries are OK. We do not recommend the use of GEL batteries except when using the WF-6800 Series. See the Owner's Manual for more information.
Can I use any battery with WFCO chargers?
Deep-cycle batteries are recommended. They can be either of the Lead-Acid or AGM type. The Amp hour (Ah) rating should be shown on the battery; for example, 120Ah. There are many battery related Internet sites. Here are some examples:
http://www.batteryfaq.org
http://www.trojanbattery.com
auto.howstuffworks.com/question219.htm
The WFCO manual for the 9500 series (50 amp input) power centers does indicate an "automatic changeover" (no physical manual switch) to select LA/AGM battery types. This is not referenced in the 8900 series literature, but the FAQ's indicate that the power center/converter the OP has in his trailer is suitable for use with either lead acid or AGM batteries.