Roof A/C Question

[Jeff Bayley]

I have my roof A/C set to "Automatic" on the thermostat meaning that the fan will cycle completely off (and on) along with the compressor when a given temperature is reached. So the whole thing goes silent, then goes back on again when the temperature starts to rise. It can on and off fairly frequently. 10 minutes on and 10 minutes off for example. Prior to cycling back on, it always makes a sound that I'll describe more as a "catching" sound than a "clicking" sound. I'm not an A/C mechanic but to try to describe best I can, I would say it sounds like a motor attempting to start or engage and it sounds like it is sticking. It happens about 3 times and then it starts on the 4th time. It is very predictable and very regular in the sense that it happens the same time each and every time. I don't know if this is a normal cycle sequence or if it needs maintenance. Aside from this, the #2 roof A/C doesn't seem to cooperate at all on the automatic mode. That one alters its fan speed from low to hi over and over and seems to be screwy. I find the “automatic” mode doesn’t work very reliably for the most part. I like to use the automatic sometimes because it gives the system a break and my thinking is that it reduces the chance of the roof A/C from freezing over. I got in their and cleaned the coils out really good but the coils on the #3 air in question seem to freeze over on occasion. Not all the time but on occasion.

Any ideas on the catch, catch, catch, start sequence or the automatic mode question ?

[Jon Wehrenberg]

Jeff,

Unless someone on this forum has detailed knowledge, I would suggest you call the manufacturer of the AC and pose the questions. I have had incredible success in getting support when I have a problem with a component.

[ken&ellen]

Jeff, I am not an AC expert, but I have rebuilt several roof top units. Freezing is usually attributed to low air flow over the coils usually coupled with high humidity. If your motor, usually dual windings, looses the high speed winding your motor may only operate on the low setting. Both the motor and the compressor are thermally protected by a bi-metal device. If this device is heating up and cooling off it could cause the cycling you discribe. My number one AC unit on my Beaver Marquis did as you discribed and I ultimately had to replace the motor....of course it happen on the hottest day of the summer!:D Ken

[garyde]

That clicking noise sounds like your condensor motor starting. It has a internal relay which closes when the t-stat asks for cooling. I am surprised to hear that both fan and motor stop at once. On my previous three coaches with roof air, the fan keeps running , and the condensor turns off when it reaches set temperture. Does the controls have seperate switch for fan control?

[Jeff Bayley]

Gary and Ken- Thanks for the reply and attempted help.

To answer, my thermastat has three settings on it. "Low", "High", "Automatic". On "low" and "High" the condensor stops and indeed the fan keeps running. On "automatic" both the fan and the condensor shuts off (on the #1 and #3 air) and on the #2 air, it operates differently (eractically) as described. I presume the #2 air has a different issue than the #3 air which is "catching" as described.