Basement ac problem

Basement A/C board:

First, no question about having a clean filter. If it can't get air you got a problem, although a simple fix.

Update on changing the board, for those who care.

Some time ago I was told my problem with the unit not working properly was a board issue and it would cost $400+ to change it. I kept playing with the unit trying to get it to work, but no luck. I read that a regular A/C repairmen could work on it but I called maybe six all passed on the idea (lucky for me because they wouldn't have done any better at it than I did). So, I purchased the board from Airxcel for about $173 including delivery. Somewhere I read that under warranty the mfg would allow one hour for the service. It took me about 3 hours to study the boards, review the instruction, mark all the wires, remove the old board and replace with a new one. The instructions for the new board 6535C320 says it replaces 6 old model boards, must be a substantial improvement?

It now seems to work well, testing in my driveway with the generator. I have not tested it in the field but I think it will be fine now.

emiddleb wrote:
Its quite possible the plugged filter caused the issue. There are various lockouts that come into play if the AC ices up, other issues can cause a lockout that resets after 2 hours. I'd certainly give it a try again before pulling off panels. When I first read this I thought of a bad thermistor wire/sensor which controls the defrost/icing cycle.

FYI, the filter should only be a basic fiberglass-type filter, the cheapest kind. The better filters that are cloth-like restrict the airflow too much and are not recommended by the AC manufacturer. I've read that a high-filter HEPA type can restrict the airflow so much that is causes issues similar to what you describe.

There are many manuals for the AC heat/pump here that might be for your unit and give you some help. Many have troubleshooting flowcharts and other schematics.

Good info; a plugged filter definitely may cause the system to shut down.

The circuit board is under a metal cover in the outside unit. You have to open the access door (hinged on top), then take a screw out of the metal cover to find the board. For whatever reason, my system has the inline fuse in the compressor fan high-speed power wire. It's not even shown on some wiring diagrams.

If you open that outside access door, be careful that it doesn't fall and smack your head. I held my door open with a bungee cord stretched around the back of the coach, but that's kinda flimsy and I never felt safe. I got smacked in the head by a door grate on a KC-135 one time, resulting in a sore head and several stitches.

Its quite possible the plugged filter caused the issue. There are various lockouts that come into play if the AC ices up, other issues can cause a lockout that resets after 2 hours. I'd certainly give it a try again before pulling off panels. When I first read this I thought of a bad thermistor wire/sensor which controls the defrost/icing cycle.

FYI, the filter should only be a basic fiberglass-type filter, the cheapest kind. The better filters that are cloth-like restrict the airflow too much and are not recommended by the AC manufacturer. I've read that a high-filter HEPA type can restrict the airflow so much that is causes issues similar to what you describe.

There are many manuals for the AC heat/pump here that might be for your unit and give you some help. Many have troubleshooting flowcharts and other schematics.

I was looking on line and found out there's a filter under the bed. It was packed solid with dirt. I replaced it so we shall see. I'm home now so I don't have a place to plug in now except for 110. I did check the breakers and they weren't tripped. Where is and how do you find the control board? Do you have pull the sheet metal off the ac unit? I'm just hoping the filter was the problem because it would start back up after it sat for awhile. Thanks for the help.

I'm in the process of changing out the boards and didn't remember seeing the fuse you mentioned, that's why I asked. I just looked for it in mine, but it does not have one. My ac has not worked properly for the two + years I have owned it. I was once told it was the board, we'll see.

rctour wrote:
gfs1943, where exactly is the in-line fuse located? Perhaps under the basement circuit board cover?

Mine is in the black wire going from the circuit board to the condenser fan. I don't have the coach here to look right now, but I believe it was under the cover. Not all the basement air diagrams show an inline fuse. I guess it just depends on the model/year made.

The wires to the condenser fan will be large, probably 12- or 14-gauge.

gfs1943, where exactly is the in-line fuse located? Perhaps under the basement circuit board cover?

The basement air systems are not all alike in their control systems, but here's a quick review of the system operation:

There are two compressors in the basement air unit. When your thermostat calls for temperature that is one degree below ambient inside the coach, only compressor 1 runs, and the condenser fan in the outside unit runs at Low speed (although I can't really tell low from high just by listening).

When your thermostat calls for temperature that is two or more degrees below ambient, both compressors run; the condenser fan shuts down briefly then restarts in High speed.

With that knowledge, here are a couple of things you can try:

First, see if you have two circuit breakers identified as "AC System 1" and "AC System 2" (may not be this exact wording). If the breakers are not tripped, turn the System 2 circuit breaker OFF and see if your air conditioner keeps running. If it does, that indicates that something is amiss in System 2 or its control circuitry. Not all systems are wired the same, but on mine there is an in-line fuse in the high-speed condenser fan wire. If the fuse is blown, the fan can't run on high. It won't automatically revert to low, so your system shuts down (probably due to high pressure because of no cooling air across the condenser).

On my system, a blown fuse was the cause. Mine uses an 8-amp glass automotive type fuse; I replaced it and the system has run fine since.

When you turn off the circuit breaker for System 2, you are taking the System 2 compressor and the High condenser fan speed out of the equation. The system won't cool as well with only one compressor running, but it will keep running and give you some cooling. If you can get the condenser fan to function in high-speed mode (by replacing the fuse), you're in business.

Be careful, and make sure everything in the system is turned OFF while you're working on it. Let us know whether this was any help.