BAC Forum
General Boards => Technical Support => Topic started by: Ron Rittenhouse on August 12, 2021, 02:31:48 AM
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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.
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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
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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
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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.
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Will look forward to rec. the Coleman t-stat information. Thanks, again. Ron
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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
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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
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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
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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
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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.
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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
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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.
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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
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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
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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
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http://beaveramb.org/forum/index.php/topic,4671.msg35204.html#msg35204
Sorry about that, computor stuff still a challenge for old techs.
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Fred,
Will uninstall T-stat again and test the wiring coming in at bottom of control panel area. If it shows no 12v hot, will turn focus to relays. If black wire shows 12v hot and wiring issue, where to start is the next question. If it's relays, would you still suggest replacing thermostat with Coleman? Will keep you posted on developments. Thanks, again. Ron
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Ron,
You are on the right tract and thanks for hanging in there. Once you figure it out, joy will be your reward!. Normally relay 5 and 6 only activate when they see 12volt from the t-stat. If a 12volt source is accidently powering up the black wire, you get the blowers. With the t-stat connected but turned off, the black wire should not have 12 volt.
I would definitely install the Coleman t-stat once you solve your issue. It has a digital read out of room temperature and set points and works well with the Hurricane furnace/water heater. Another feature is if left on "auto" and it calls for cooling, it only turns on compressor #1 to try and maintain ambient temperature to save power. If not satisfied, it turns on compressor #2 also to satisfy your set point. Blessings, Fred
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Fred,
Thanks very much. Worked yesterday, but plan to use probe tester on black wire today after uninstalling t-stat (again). If black wire hot, will try to track down why. Sincerely hoping it's relays. will let you know. Been trying to focus thinking in this direction: Phil. 4:4-7. Blessings,
Ron
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Hey Ron,
Enclosed please find some pix of the T-Stat wiring as it enters the air conditioner @lower right side corner. You will notice that there are 3 spare wires that are not being used. Brown, Green, and white. In the event the black wire picked up 12 volt from an unknown source, you can isolate it at each end and then use the brown wire to replace it. If the #5 & #6 relays are stuck in the run position, you will have to replace them.
When my outside blower relay failed on my PC board, you can see where I temporarily installed a cole hersey 12 volt 30 amp relay so I could use the coach air conditioner.
Best part about Phil 4: 6-7 it is my favorite verse and He has the Power to guard my Heart. Blessings, Fred
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Ron, here is the other 2 pix
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Greetings,
For those folks that are following this post and have the SCS basement air conditioner, we have traced the failure to the PC board Relay #RL-2. It is the relay that controls the evaporator and condenser blower motors. It is a common failure on the board. The part # for the relay is RH4V2-U-DC110V. Hope this helps, Fred