Original message
| mafen
 |  "Applied Air Systems SJAT SINGLE"
, posted Mon 15 Nov 10:01  
Hi, we recently had an Honeywell T42 1018 thermostat die on us at our company and we're all perplexed about exactly which thermostat we should get to replace it. Our unit is a forced-air heating and cooling Applied Air Systems "SJAT SINGLE" unit. What thermostat could we replace it with? I have a wiring schematic here, and it lists the wires as R, Y, and GY going to the thermostat. It also lists a 'BL' that is labeled 'Not used'. Behind the thermostat, however, there are four wires, labeled R, Y, G, and B. Pretty confusing... any suggestions on what to replace it with or how to replace it?
-Mafen
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Replies:
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| pilight
| "Re(1):Applied Air Systems SJAT SINGLE" , posted Sat 27 Jan 14:09
You probably have found a solution by now but a simple way around the dilemma of using a high voltage thermostat would be to use a Honeywell Fan control center which can switch two different loads
i.e. w and g and has a low voltage transformer built into it that can be used with a low voltage thermostat. Those connections are on the outside, the high voltage are contained within the J-box. If r
and b are 110 vac, (then wired in the j-box), the w,g,r,y and c terminals on the outside can be used for any low voltage 24vac applications you need. If fan and heat need to be operated independently and additional relay will need to be configured into the control schema.
Pilight
pilight
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| Xenos
Webmaster 
| "Re(1):Applied Air Systems SJAT SINGLE" , posted Mon 15 Nov 20:51
You have to use the same as thats a high voltage thermostat. Most thermostats can only handle 24vac.
Xenos.
The best way to escape a problem is to solve it.
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| | mafen
| "Re(2):Applied Air Systems SJAT SINGLE" , posted Tue 16 Nov 11:47
More information...
The unit is a Applied Air SJAT SINGLE Serial # 2000-79611
The heater is a 'Air Turnover Heater',
The power supply is a 230 volt 1 phase 60 hertz.
The gas burner is a 160 MBH output w/ natural gas @ 7" inlet pressure.
This unit does heating and cooling.
The previous thermostat was a Honeywell T42P 1018, which was discontinued 7 years ago and Honeywell does not have a direct replacement reccomendation for me.
The wiring schematic has the terminals R, Y, and GY listed as connected andd BL listed as not used.
On the back of the T42, however, there are four connections, labeled 'R, W, G and B', not what I originally thought - my mistake. Any specific model numbers I could give my boss to get a replacement for it? I'm totally lost here in HVAC land...
-Mafen
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