Basement A/C units run constantly

[Ron Rittenhouse]

My 2000 Marquis Jasper has the dual 27k BTU basement a/c units.  Units cool coach fine, just won't cycle off.  Even with coach power off, thermo set to OFF, anytime we plug in or start generator, a/c immediately runs and stays running.  Having trouble finding shop to address.  Any ideas? Thanks is advance.

[Eric Maclean]

Ron
It sounds like something is stuck in the control circuitry perhaps thermostat or a relay  .
I'm not all that familiar with the basement systems so I'll let someone else step in here with suggestions.

Eric

[Fred Brooks]

      Ron,
 I have the same unit and the weak links in the system is the PC board and the original thermostat. Before we go too much further, are both blower motors running? The evaporator motor is the one blowing cool air into the coach, the condenser motor is the one blowing hot air out under the coach. If both motors are running, try disconnecting the t-stat. I am including the schematic to show the wiring and motor relays on the PC board. Not sure if you are a hands on guy with a digital meter to check it out but any good tech worth his salt should be able to determine the issue. If it turns out to be the relays on the pc board, they can be replaced. If it is the T-stat, I will look up the Coleman t-stat that replaces the original one. Let me know, Fred

[Ron Rittenhouse]

Thanks, Fred...will try tinkering with thermostat today. have call in to rv tech, will if he calls back. Yes, both motors are running simultaneously.

[Ron Rittenhouse]

Will look forward to rec. the Coleman t-stat information. Thanks, again. Ron

[Ron Rittenhouse]

Fred,

Disconnected t-stat and re-applied shore power.  Both motors started immediately as before.  PC board issue?  Have not heard back from rv tech I called.

Ron

[Fred Brooks]

   
  Ron,
If you go outside and open the water bay, on the left side is the air conditioner control box. remove the cover and in the center on the left side you will find the plugs for the two motors. The top is the evap blower and the lower is the condenser blower. Unplug the coach, and unplug both connectors. The relays just to the left of each connecters control the motors. When mine went bad, I temporarily by-passed them with some 30amp bosch relays until I could get the relays replaced on the PC board. Let me know. Fred

[Ron Rittenhouse]

Fred,
This is very helpful, even if it's just to show a repair tech. I will inspect the control board area and get familiar with it. May have a friend who will be able to test the relays to see if there's a malfunction.  Thank you, again.
Ron

[Ron Rittenhouse]

Fred,
Opened up control panel for A/C and see where power connects to top and bottom blowers.  Have photo of layout I would like to send. If you can identify which are the relays that should be tested, a friend can test for me.  If we find the problem, would the replacement parts be available through SCS? Please let me know if the photo does not attach.  Thanks, again...Ron

[Fred Brooks]

   Hi Ron,
  That be what we are talking about. About 2/3 way down you will see 2 brown plugs with a white, black, and red wires coming out of it. Carefully unplug each one and then plug the coach back in and the air conditioner motors should not be running. The black relays just to the left of the plugs are the relays activating those plugs.
  The company that used to rebuild those boards (Flight Systems) is closed. These boards are really easy to repair because they are analog with NO chips or programs. The thermostat does all the logic. If the relays are the issue, you can find replacements on google and order them. I can tell you many of these SCS air conditioners have been replaced because of a $5.00 relay. Replacement Air conditioner from Coleman can cost $5000.00 installed.

[Ron Rittenhouse]

Fred,
Unplugged both brown plugs, reapplied power, no blowers running.  To test RL5 and RL6, do I need to pull board loose and drop it forward? It appears they are soldered on the back of the board and do not unplug. Thanks again for all this assistance.
Ron

[Bill Lampkin]

I'm not familiar with basement A/C systems, but I have worked with relays over the years. My guess is that the relays are ok, as they 'reset' (switched off) when you removed the power. Relays can be 'bad' if their contacts weld together (thus not resetting when power is removed) or the relay coil can burn out (open or bad coil). Other than that, relays are generally pretty reliable and trouble free. I would look to the t-stat for issues, or maybe some other component on the relay circuit board.

[Fred Brooks]

   Ron,
 Here is where it gets a little complicated. The cover you removed to access the relays has the schematic label on the back side. Let me start by giving you the sequence of commands coming from the thermostat. Focus on the thermostat wiring.
When the thermostat calls for cooling it sends 12 volt power to "GH", and "Y1 & Y2". This turns on the relays that control the 2 blowers and the 2 compressors. Either the 2 relays in question are stuck in the "on" position as Bill suggested or the relays are energized by accident. If it were me trouble-shooting the issue, I would check the wiring coming from the thermostat. The T-stat wiring comes into that compartment on the lower right side and sometimes becomes abused by storage and could be chafted at the romex connector. I would take a 12v test light and probe the black wire and see if it is 12volt hot even with the t-stat disconnected. If it is, you have a wiring issue. If not then the relays are stuck. If it is the relays, order replacements, un-solder the old relays and install the replacements. Fred

[Fred Brooks]

     http://beaveramb.org/forum/index.php?action=search2
  Ron, Here is the link to the Coleman thermostat, scroll down to the #3 comment from Steve Huber concerning the wiring. I put this T-stat in my coach and it works excellent. Fred

 

[Steve Huber Co-Admin]

Fred,
Your link only takes us to the Search page. Please go to the post, open it and then copy the liink.
(I looked for this post yesterday and couldn't locate it).
Thx Steve