Attic Split Air Conditiong System Blower Won't Shut Off Problem ?

Hello:
Have moved into a 30 yr old house that has a split type of air conditioner in the attic.
Have never had one before, and would like to ask the following, regarding a problem that I can't dope out.
The unit has the condenser outside, and the evaporator section, and apparently a blower in the attic. Attic space is very low, and just about impossible for me to crawl in and examine what's there, exactly.
Anyway: When I turn it on, it the A/C seems to work. The only problem is that I cannot get the attic blower to ever stop running. The only way seems to be a typical wall type switch in the attic which shuts the AC off totally for the blower. Obviously, it's meant for turning the AC for servicing, etc.
The unit is controlled by a TRANE brand thermostat, that looks pretty "typical." Has a dial for temp., a thermometer, and a slider with 3 positions. These being: FAN in the upper position, OFF in the lower position, and AUTO in the middle position. None of them seem to effect the blower's running.
I guess, but am certtainly not sure, that it might be that the thermostat slider has welded contacts as it is probably about 25 years old by now, or a "stuck" relay (in the attic blower assembly, or possibly in the condenser unit outside-not sure where they place the controls for this sort of thing ?) somewhere, or... ?
Any thoughts on this would be most appreciated.
-Would sure like to have the thermostat work things, normally. -Should i buy a new thermostat ?
Much thanks, Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If I had just moved into a new house I would have my Hvac completly serviced. You dont know what other issues you may have and only a complete check up can tell you. This is not a time for DIY.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.