1986 Toyota Camry

Engine Cooling problem
1986 Toyota Camry 4 cyl Front Wheel Drive Automatic 210, 00 miles

When driving to work this morning(temp 75), went approx 3 miles and temp was ok (gauge at Half), but in the next 3/4 mile suddenly went up to H. I parked it and walked the rest of the way.

Coming home (temp 95), it did fine (Guage at half).
1--I DID have A/C on on the way home (and both fans were working)
After I got home, I noticed both fans were running.
I turned A/C OFF and neither fan was running (gauge still hovering around half).
2--Had NEW Radiator cap both times.

Would this be thermostat or temp sensor to control fan---How can I tell the difference?
July 29, 2008.

Temp sender located near thermostat housing pull plug and jumper fan on replace no fan check relay

Jul 29, 2008.
Thanks for your advice---will check it.

Jul 30, 2008.
1986 Camry LE with 2.0 2S-E engine. 210,000 miles.
New Radiator Cap 50/50 coolant mix

Unplugged fan relay and both fans came on.

I noticed bottom radiator hose was much cooler than top, soI replaced thermostat (not OEM) with 180 degree. Did fine for 3 days.

Then, Saturday morning going to work--it must have overheated as some coolant was on ground. On the way home ran almost to H --(I was ready to pull over AND had " Heater" blowing hot to vent off some heat). After it cooled I looked and radiator is dry--again some coolant on drive.

Note: New thermostat did NOT have vent hole.

Any ideas what's going on?
Thanks in advance for any help.

Aug 4, 2008.
If it ran fine for three days then got hot with coolant loss. Then maybe there is a slow leak. Have system pressure checked to identify any leaks. Also check oil any discoloration and oil filler cap any moisture or chocolate colored substance in cap?
Let me know

Aug 5, 2008.