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Old 09-22-2021, 08:29 AM   #15
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Originally Posted by Ray,IN View Post
How then do you refer to return air into the plenum? That reads like you forgot what you learned 50 years ago.
Had a strange name for it... called it the "return air temp" vs. ambient temp. The return air temp is the temp at the intake of the AC unit house or car. the problem with auto ac is that often the return air is mixed from the outside "vent" door and the inside return air intake. I often screw closed the outside vent door and tape it over to seal it is to prevent hot air entering from the engine compartment on gassers. This works on DP's with front gen sets too. I like to install a "cabin filter" over the inside return air intake on moho's when ever possible as it cuts down on the dirt floating around and allows the AC to reduce the allergins in the air. On house AC's the delta t is often about 30 degrees but auto ac is diff because of how close the evap coil is to the supply vents, usually less than 18". the evap coil temp usually runs about 10 degrees and supply/vent air temp should be about 40 degrees depending how long the supply air duct is. Mine is 38 degrees, center vent, idling, 100 degree outdoors, outside the coach ambient temp... when I'm going down the road it gets down to 36 degrees.

House ac is the same in that you still have a 10 degree evap temp on the coil but you are moving a lot more air volume over the evap coil so by the time it gets to the supply/registers it is much higher temp so the delta t is less. 12" ducts running as far as 80 feet you just can't get more than 20 to 30 degree delta t. Old guy who taught me ac told me to think of it like cats... one is a house cat(auto) the other is a lion (house)... all about controlling the volume that is moved so as you don't move too much "air" over the evap coil and get warm air, or a pitiful delta t.

I don't mean to insult anyone, but if a dog is barks I call it a dog. If it meows I call it cat... if it does both I call it a politician...

So, figuring I must have lost a couple of marbles I googled ambient air temp and guess what it comes up as?

Ambient temperature is the air temperature of any object or environment where equipment is stored.

Description The storage temperature (Tstg) refers to the temperature at which the device can be safely stored when the device is not powered. The ambient temperature refers to the temperature of the surrounding environment (typically air) when the device is powered.

Ambient temperature can be very different from room temperatures, such as in an unheated room in the winter or an unchilled room in the summer.

Think of it like "root planning" how do you plane a round root of tooth.... you don't, planning is a term use to refer to smoothing wood and metal to a flat surface to prepare it for sanding or polishing... Some dentist decided it would be easier to sell "root planning" rather than "root scraping" so he decided to apply it to a inappropriate application.

Google, copy and paste are amazing tools... the above statements are all from diff sources.

AND... the stuff that comes out of the vent we called the "supply air" so there was the "supply air temp" slang= vent or register air.....
May your black water hose never break!
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Old 09-22-2021, 09:04 AM   #16
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Ok, now back to the problem... first check to see if the AC clutch is activating. if not then add B+ the compressor wire to activate the compressor. Next while the clutch is running does one of the hoses to the evap cover get cold? If no then the ac charge has failed. If yes then the compressor and charge are good. Next check to see if you are getting a compressor signal from the wire that you disconnected from the wiring harness that runs to the compressor. If so, then the 12v portion of the switch has not failed. If no, have you tested the 12v supply to the switch???? the switch is combo 12v and vac switch.

next I'd use a vac gage and check the lead from the vac resevoir to the switch, if you have vac then the vac switch portion has failed. In some cases you can rebuild the switch, others it is a waste of time fooling with it.

Diagnosis.... You need to identify what has failed, compressor, compressor clutch, blower motor, vac air supply, vac switch, coolant charge in AC, heater coolant valve.... there are many parts the system, none of the parts are complicated but you need to test each one.... OR... you can do like a lot of folks do and throw a 5 gallon bucket of money at it by replacing one part at a time until you get the right one...

Sounds like you are off on a new adventure to leaning about AC systems, read, take your time and the study will serve you for the rest of your life...

Liability warning According to some sources, because I'm an old guy and can't regurgitate the written data in an HVAC textbook, I'm not qualified to give advice...
May your black water hose never break!
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Old 09-22-2021, 02:28 PM   #17
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Originally Posted by semcha View Post
I have a 1994 Itasca Suncruiser on a Ford F53 chassis. It looks like I need to replace the dash AC controller because changing the settings on it doesn't affect the vacuum on any of the outgoing lines. So my vent doors don't open and close, and I don't get cold air, even on MAX AC. The vacuum hose going to the unit is good and does pull a vacuum.

Problem is, this is an old system, so I'm not having a lot of luck finding a decent replacement. Anyone have experience with this?


Donít know about your dash air problem but I did figure out how to run both roof airs at same time on my 1995 suncruiser.
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dash, itasca, suncruiser

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