steve morris

If the duct on the left side is the return duct, the room the a/h is in now is a "RETURN PLENUM". Every thing in the room must be plenum rated and the room should be sealed 100 percent. Cracks anywhere will let air in. The return air should only enter through the return duct. The dirt is in the house, the a/h only blows it around. FILTERS!

Here in the DEEP SOUTH (FL) your higher eff. furnaces such as 90% you must use plastic pipe to vent the flue due to the category for the appliance. It's rated as a condensating type. A lined chimney with tile or metal would not meet code, and would not last. Read the flue sizing charts in the fuel gas code, the main thing is btu's(heat) and length of flue. There are four categorys of vented appliances, non positive pressure and positive pressure flues flues. condensating and non-condensating(see the definitions in the F.G.C.).. Even here a clay lined chimney has to be very small for a furnace to be vented into it. It takes so much heat to warm the liner up for the draft to start, most of the time you just puddle condensate at the bottom.

After looking at the picture again if the red color on the corners of the angles around the dampiers is fire caulk make note of it per most mfgs. no fire caulk is allowed, some of the fire caulk is intersermesent(probely spelled wrong) this means when in a fire it will swell up several times it's size to seal the hole.

The dampiers in the duct have fuse links aprox. 160 is the temp. they trip at. When you have a rated ceiling, where the grills are on the surface, the dampiers must be a "CEILING RADIATION DAMPIER" they are different. If you can access them enough, they have a small tag on them telling you the hour rating,(1.5 to 3 hr.), the mfg. of the dampier, and who is the testing/listing agency. The have very specific mounting instructions. Several web sites can give you lots of info.(MIAMI TECH.,LLOYDS, RUSKINS all have their instructions and general info on them). ON another note the pics. you sent, the duct work dosen't seem to be sealed at the joints. If this is a garage, this is very important due to carbon monoxide. Here in Gainesville, FL. we hade a death due to a car left running(accident)in the garage, The old man was inside the house, with the a/c running. The return air had many joints in the duct none sealed.. This is part of our bldg. code and energy code.

Check out the spec. on CPVC(flow guard gold to be exact) they require 18" clearence also(gas water heaters) and about a million other items that are on their list(not 18" just no contact). Go to one of their CEU classes sometimes. You can contact you local FAPGMI chapter if your in florida.

Try the ACCA website.

On a TRANE unit of that vintage the mfg. uses the start winding in the compressor as a crankcase heater.(I believe this is a bad idea,Florida being the lightning capital of the country, a lot of shorted start windings) The temp. you stated is a little high, it may have other problems and the compressor is cyling on the internal t-stat embeded in the winding. When the control contactor goes bad some a/c tech.(for lack of a better name) may have miss wired the new one in, I found them all the the time when I was in the business.