Roof air woes

[kyle4501]

Had a great weekend camping, except for an issue with the roof air.

It is a Coleman unit with the 'warmer - cooler' thermostat knob on the right & a fan knob on the left. The fan selector allows hi or lo choices for cool or fan only. There is a heat selection too.

It seems the problem is the compressor stays on continuously - which lead to the evaporator coils freezing over. I switched over to 'fan only' & in 30 minutes, the volume of air from the unit returned to normal. I then turned to 'low cool' & the compressor came on & stayed on - never cycled. The temp dropped continually until I turned it back to 'fan only' at 65F room temp.

When I have time to open this thing up, what should I look for? (I haven't found the manual yet, but when I do, I'll need to verify it is for this unit & not the one it replaced . . . .)

Thanks. . .

[Jerry32]

Your warm -cool should be the thermostat. If it is set too cold the compressor runs onger times. Have you tried the warmer setting?

[kyle4501]

Good question, yes, I did try several settings.
It was on the warmest setting when it was 65F inside & it still left the compressor running.
In the past, you could change the temp knob & hear when the compressor cycle on/off.

Is the temp circut at fault? or is there a relay that is stuck? or . . .

[Airbag]

Seems to be a common problem with these things. I have two new Dou Therm units, One is made in Mexico and the other Virginia. The Mexico ones in the back ices up. I believe the key to preventing this is to turn the temp up higher and leave the fan on high. When mine cycles the fan and compressor shut down. This is not as conducive to melting the ice as fast as having the fan stay on. You will just have to find the sweet spot that works best for your unit. I hope that is all it is. Good Luck

[Hartley]

There are two common problems with roof air temperature control.

The sense tube is usually located up around the air intake and can become loose
or move away from the airflow. It can also be damaged during cleaning or even kinked which will stop it from working.

The thermostat switch can be faulty - Most only last a few years at best. The contacts will arc and fuse together and you only have 2 choices, Either replace the whole themostat and sense tube assembly or try to take it out and find a way to clean up the burnt contacts ( not always works! )

A third and most common problem is that you are pulling wet air into the coach faster than the a/c can remove the water. With a weak thermostat this can cause ice to form and after it starts it will eventually freeze up the coils. (setting the thermostat too cold will do the same. )

Even with a good thermostat if the coils ice up the airflow is stopped and the compressor will continue to run until the head pressure causes an overload and the breaker will trip.

I still find it funny that people think that setting the thermostat lower will make it colder faster. Maybe somewhere they do that but never in an RV air conditioner. They just ice up and quit working.

Your arch enemy is moisture and condensation. Too much moisture due to roof vent fans running or open windows/areas and what little 10 X 15 spot of very cold coils will just clog up. ( cat hair and dust bunnies also are a pain! )....

Hope that helps....

[kyle4501]

The temp switch used to work.
Now, it doesn't.

Used to be that at 1/3 from warm towards cold, it would cycle the compressor with a room temp of ~80F.
At 2/3 form warm towards cold, it would cycle at ~70F.

It froze up in the pre-dawn hours Saturday morning after reducing the inside temp to ~50F (Wife & kids were cold & under quilts).


The compressor isn't cycling off when the fan switch is in the cool mode, regardless of the temp knob setting. (It used to, so this is a new opportunity.)


I will take the thermostat apart & see what I see.

Thanks!

[Nick Badame Refrig/ACC]

Hi Kyle,

It could be that you are short on refrigerant! Follow me here...

When you are short on refrigerant, there will be a section of the evaporator that will Not refrigerate "usually the top" and

a section that will refrigerate too much "Usually the bottom" causing frost over. Now, look to see if your sensing tube for your

t-stat is at the top of the evap. or the bottom. If at the top, the t-stat will never be satisfied and never shut the compressor off.

Just a possibility
Nick-

[kyle4501]

Thanks Nick,
I'll look for the location of the sensing tube when I open the thing up.

You're right, low freon can cause some strange things to happen. 


Now, how do I cool the interior down so I can work on it . . . LOL!

[uncle ned]

Kyle 

drag that air stream up to Linville Falls campground this week end and i will help trouble shoot it.

Won't need air there and a great place for the kids to play.

uncle ned

us old people can camp for 6 dollars

[Nick Badame Refrig/ACC]

Hi Kyle,

To test your t-stat, on a 75 deg. day or higher, remove the two wire terminals on the stat. Then using a continuity tester, or OHM

tester, put your two probes on both terminals of the stat and turn your stat knob both ways. You should get continunity one way, and no

continunity the other way. If open both ways or closed both ways, the stat is bad.

Good Luck
Nick-

[kyle4501]

I opened it up this evening. A little dust, but nothing more than a light dusting.
The t-stat sensor tube senses the return air temp. It didn't look out of place or damaged.
I vacuumed & cleaned everything & put it all back together & tested it - same thing, compressor won't cycle off.

I took the cover back off & looked closely at the pickup tube & opened up the t-stat junction box - no evidence of smoke or water damage.
So, now I'm trying to decide if the plastic wire connectors have one more R & R left when I decide to try a piece of ice on the end of the temp tube. I turn the unit back on & try the ice.

I didn't know how long I should try this, so I decided to hold it there as long as the ice cube would last. (the cold water felt better than the sweat . . . .)
After almost a minute, the compressor cycled off. I removed the ice & after a bit, the compressor came back on. I got another ice cube & the compressor cycled off much quicker this time. I tried several more times - at 5 minute intervals with the same results.

While I was playing with the ice, I noticed one of the bolts didn't look right - yep! It was loose, it had backed out almost 2 inches! 
I left the A/C running while I removed another panel to access the bolt to re-tighten it & check the other two. I noticed the air was not cold, so, after the initial "aw crap" passed, I turned the temp knob a little towards cooler & the compressor came on. 

I stayed out there for another 30 minutes & it continued to cycle as it should.


I guess I'll play a cheap skate & see it it acts up again before I look into replacing the switch.


Thanks for the assistance in trouble shooting this - made it easier to dive in.

[Len Silva]

The only way to insure that it won't act up again is to buy a new switch and have it ready to install.  The old one will never have another problem.