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Old 12-01-2018, 10:02 PM   #1
Bus Nut
 
Join Date: May 2018
Location: topeka kansas
Posts: 468
Year: 1954
Coachwork: wayne
Chassis: old f500- new 2005 f-450
Engine: cummins 12 valve
Rated Cap: 20? five rows of 4?
cadillac - continue ac discussion

so what about thermostat for cabin temperature.... controller for the solenoid? I wonder if there is an off the shelf unit that could control a liquid line valve, and fans. The front vintage air heater/defrost/ac firewall mounted unit is all electric and will be operated by the driver/shotgun. The rear could have some sort of manual controls driver override with an automatic temperature control at the rear. You seem to have more experience with "custom" ac set ups.

I am certain I can do ducting to feed the back side of condensors cool air from under the bus. Have you seen highpressure line with fins? Might as well use some sort of hard line from the front to the rear with cooling fins, it will be a run of 15' or more... wonder what kind of temperature drop I can get... The way I do air flow is yarn testing and watching air flow. or in a tight spot under I can use a camera. i wonder if can suck air from the side, and use that air behind the rear end to smooth trailing side air flow..... I will have do some testing to see what works or what I can make work in terms smoothest air flow. I could do a water manometer and look for high pressure zones to feed the condensor and go from there. Still work to do.

but, this is the kind of stuff i really dig.

william
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Old 12-02-2018, 08:34 AM   #2
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 10,231
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
most of the skirt condensors suck air from the side of the bus and blow it out underneath... the fans are reversible. and ive seen rare occurances with systems built opposite.. in my experience the air is always hotter underneath the bus.. not only do you have engine heat from your own bus. but pavement heat swirling as well.. pullin g in from the side keeps my liquid line temps down just a few degrees over ambient..



ultimately you dont necessarily want to cool the hot gas discharge line from the compressor too much or you run the risk of liquid in the compressor cylinder..



most of these bus A/C units have a "room" sensor in the evaporator return.. its a simple thermistor going to the control board.. adjustable at the driver control.. some like my trans/Air its just a 3 position. "cool / cold/ coldest" setting and a off-lo-high for the fan.. you can get fancier electronic controls..



the controls im using on my DEV bus are electronic.. made my ProAir LLC.. they are digital electronic.. heat / cool controls.. I have the heat side turn the water on / off to the controlled evaporator and the A/C side turns the compressor / valve. on / off..



they are pretty simple in operation, they engage a relay for the compressor and a relay for the condensor (2 separate). when there is a cooling call.. this is great because with 1 compressor 2 evaporators, 1 condensor.. you can use the compressor output on each control to operate the liquid valve.. a diode circuit on the condensor output of each control can be used to control the condensor and compressor together .. so that way whiuchever control is calling for condensor kicks them on.. if neither are calling, the compressor kicks out and both valves are opened using normally open valves means you need an opposite relay to close them when the zone is not calling.. you energize to close... so you run a feed lead from the output of the condensor/compressor relay to the coil of each valve relay.. what this does is only allow the valves to close when the compressor is running.. you dont want to close both valves when the system shuts off.. you want free flow equalization..



so normally open valves.. energize to close..



does this make sense? I dont have a good drawing of it.. i kind of built it on the fly..
-Christopher
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Old 12-02-2018, 10:31 AM   #3
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Is there a flow chart out there to troubleshoot my factory Carrier AC?20181129_203426.jpeg
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Old 12-02-2018, 11:44 AM   #4
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
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Year: 1991
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Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
here is a link to the install manual for that ducted system... it might help you determine where components are... what does it do? turn on but not cold? no fans no lights?



https://www.transarctic.com/media/do...mh9r7u92td.pdf


https://www.transarctic.com/media/do...2curmm8zzq.pdf


carrier-ax.pdf


-Christopher
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Old 12-02-2018, 01:52 PM   #5
Bus Nut
 
Join Date: May 2018
Location: topeka kansas
Posts: 468
Year: 1954
Coachwork: wayne
Chassis: old f500- new 2005 f-450
Engine: cummins 12 valve
Rated Cap: 20? five rows of 4?
tm21 vs enhanced sanden

You seem to advocate the sanden.... are you running a single compressor? with more than one evaporator? my bus is set up for 10 people, it is just barely under 24 ft ... If I remember 748 cubic feet. If suggested charts are correct in 100 degree to 105 degree, I should use about about 51" of skirt mount condensor with the fire wall and rear mount evaporators......

aim for a worse case scenario... I see the skirt condensor as being a little large but will not be a limiting point for performance, performance gage being how cool I can get the inside in the 100 degree temps, want to keep the hooligans happy. with what you described, do you have some sort of zone cooling?

I would have to interlink the vintage air dash unit and the rear unit temp controls, I dont see this as difficult. You using the temp controls to activate a relay and the relay then controls solenoids. thinking along the lines that have some sort of voltage pulse from the solenoids and the relays protect controls from collapse of coils from solenoids. what about accumulators in front of each evaporator?

Am I following you correctly?



william
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Old 12-02-2018, 06:08 PM   #6
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 10,231
Year: 1991
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Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
my DEV bus is a short bus.. 7 row.. oine compressor and 2 evaporators..



un my case there was no bracket kit made for a TM-21 anymore.. and I liked the idea if I blew a compressor or a belt i could swap it quick..



so learn from my mistakes.. I located my condensor under the bus and too far forward instead of in the skirt.. my liquid temperatures get up there only because im sucking alot of hot air in.. ive put sensors on the air intake of the fans and at times im sucking 125 degree+ air in.. that isnt going to keep things very cool.. when the airflow under the bus is good i get right cold air..



I ran into the issue of one evaportator turned off andf the other on... namely running my dash air and not the rear.. the dash air evaporator. actually gets colder air.. by about 10 degrees if i turned the fans on to the rear.. thats when I watched my suction line temp and pressure drop because that rear unit weas still flowing refrigerant.. every TxV has some sort of minimum. and so I was busy slowly making ice as its minimum was enough to really drop the whole system suction pressure..



once i installed the valves things got much better.. i could get that ice-cold air out of my front with the rear turned off..


im running a 60" condensor.. #12 suction, #10 discharge, #8 liquid main.. and a #6 to each evaporator after the 'Y'.. my evaporators each have a #10 coming out as suction.. so that 'Y'. takes 2 10s in and a 12 out.



I think thats the line sizes you'll use with your TM-21.. although your large evaporator may take a #8 liquid.. your dash air will probably be #6 liquid and #10 suction..


controls - my controls both of them provide relays for all of their outputs.. so I dont need to worry about driving the relays with transistors.. although i hadnt thought of relay arc on shutdown from driving another coil with the contacts of the control relays.. .. though I hasve diodes in place to prevent back-feeding the controls when one unit turns off and the other is still on.. that should prevent back-current..



this is the control im using.. there isnt mucb online about it.. but if you get interested ill scan the manual for it asnd itds controller board.. the onkly disadvantage to this is natively i couldnt run my heat and A/C at the same time on the sane unit.. (a bif advantage of dash A/C is the ability to refrigerate and dehumify uop front). so I had to put a switch in to force the A/C on when im in heat mode.. at that point the only thermostat controlling the A/C is the freeze thermostat.. it will cycle the compressor against a 31-32 degree coil..



the heater control just turns on and off the water valve to that unit.. I have all my heater cores run in parallel so each one can be turned on or off.. the exception being my right-front and far rear heater both have flow anytime the main heater valves are energized (a switch on the dash).. but those units are heat only so no need to kill the water to them individually..



on that bus i also fought engine heat fiercely.. this summer I finally discovered why.. when I dropped out the AT545 for my 643 swap.. I found that the navistar to Carpenter marriage was done shoddy at best.. allowing full engine compartment heat to go between the metal b ase floor and the plywood.. since that plywood had a gap that meant engine heat came in and went up the main supports.. came from under the floor, etc.. i sealed everything tight i had thought.. well now we will see this coming summer how it does.. I got the new trans in but havent road-tripped that bus in hot weather yet..

-Christopher
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