Main AC no cold air

Rigged

Member
Joined
Jul 5, 2023
Messages
13
Hey Folks!

I've been searching for a few days to get some details on the outdoor temperature control board for my Coleman Mach 15 AC/HP (48000 series). I've got no cold air coming from the unit, and I've done a bunch of troubleshooting. However, I'm stuck on what exactly to test to determine the problem which I suspect is something with the Outdoor Temperature Control Board.

Outdoor air temperature: 90*F

Main AC (Center) (problem unit)
  • 82*F at return
  • 83*F at nearest vent (probe)

Secondary AC (Garage)
  • 86*F at return
  • 62*F at nearest vent

Troubleshooting steps:
  • Compressor not running
  • Fan high/low operating properly
  • Thermostat working correctly
  • Tested capacitor (uF) (good)
  • Tested compressor (ohm) (good)
  • Output of the lower control board was 115VAC coming from the purple wire to the Outdoor Temperature Control Board
  • No AC output on the outdoor temperature control board (black wire to the compressor)
  • Removed coil sensor
  • Close coil sensor ports
  • Bypassed the board and connected purple and black wires (similar to my other AC units without the outdoor board), and compressor ran as expected

What the heck does the board do? It has another orange wire that routes to the two ports on the lower board meant for a heater (which I don't have)

Thanks for any help!

Kyle

IMG_6016.jpg

Factory image:
Temperature control board.png
 
Last edited:
[MENTION=56334]Rigged[/MENTION],
I would remove the control board and look for any damaged components. Swollen diodes, burnt resistors, swollen caps.
Can you verify that the relay is operating? AC power into the relay?

My guess is this board is just a relay control board.
- transformer 110VAC to 12V or 5V AC
- D1-D1 bridge rectifier
- R7 current limiting resistor
- C1 filter cap
- U1 voltage regulator
 
Thanks [MENTION=42862]Casa_Woody[/MENTION].

I removed it and don't see anything abnormal. I did verify that there is 115VAC coming into the board on the purple wire with nothing leaving which leaves me to believe the relay is bad, but I'd like to determine how it is triggered. My assumption would be the THERM-1 and THERM-2 being open/closed (which I've tried both)

Temperature control board volts.png
 
The upper terminal in the picture should be the NC terminal which should have 120V on it if the relay isn’t actuating. With power off, measure resistance between the input terminal and the two other spade terminals. On the back side of the board, there should be 5 pins connecting to the relay through the board. Three will be the same points as the spade terminals. The other two will be the coil,which should measure ~640 Ohms, possibly different in each direction due to a diode across the coil.

ETA: There may be more through pins which have no electrical function, but are just for mounting.
 
Concur with what [MENTION=10506]jkwilson[/MENTION] stated.

Your updated picture confirms the relay is bad. Mechanical failure in the relay. The coil in the relay is most likely good, but not able to actuate the failed relay.

This is how I believe the relay is actuated.

Transformer 110VAC to XX-VAC
D1-D4 bridge rectifier (AC-DC conversion)
C1 Smoothing Cap
Z1 is zener diode which is a poor man voltage regulator needed for U1
R7 limits the current so Z1 does not blow like a fuse.
Therm 1 is power to a sensor (thermal cut-out) and 2 is the return from that sensor (i don't think it matters which way it connected). The return is routed through a resistor R1,4,5,6,8 ??) to U1. U1 is a gate controller and based on input from senor will actuate Q1 to either energize / de-energize the relay coil.
 
To close up the thread, the board was, in fact, bad. It is a discontinued part, but I contacted Coleman (Airexcel), and they sent me a replacement.
 

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