Air Conditioner

Almost a year ago, in the message about picking up our LD (#8184 and #8185) I mentioned how our A/C froze up and how it didn't really have enough capacity.  During this summer the problem reoccured while we were at the Life On Wheels conference in Moscow, Idaho.  Up to then,I had accepted the way the A/C worked as a fact of life.  An instructor at the conference assured me that freeze-up was abnormal so I asked Steve at Lazy Daze what to do.  At his direction, I contacted Dometic and got the name of a local dealer from its automated phone system.

It turned out to be cool, about 70-75 degree day.  The local dealer noted that it was freezing up as A/C's may on a cool day and that the split temperature (the amount the inside air gets cooled by a trip through the A/C with the blower on high) was 17 or 18 degrees.  Everyone said that the split temperature is supposed to be 19 to 21 degrees and the A/C was drawing about 11 amps.  The temperature was almost OK and Dometic was slow answering my dealer's call and I needed the coach the next day so I settled for paying for (it was outside of warantee) a thermal switch to turn off the A/C compressor when it froze up.

I am a professional electronics engineer, but don't know that much about A/C.  But after the dealer visit I understood what measurements to make and what they meant.  So a week or so later when a hot day came I repeated the measurements.  On a 90-95 degree day the split temperature had fallen to 15 degrees and the A/C was still only drawing 12 amps instead of the 15 it should have (with a 115V line). 

AC units are specified at an outside temperature of 90 to 95 degrees so when the split temperature is specified as 20 degrees and I measure only 15, that means I was getting only 3/4 of the cooling capacity I had paid for.  With the data in hand, I asked Steve at Lazy Daze to help me contact Dometic which he did.  I talked to two people at Dometic the rep. Roger, and then the tech Al.  They thought the most probable problem was that there was insufficient refrigerant in the A/C's system.  The upshot was that Dometic authorized replacing the A/C, which was done last week by the same dealer as before at no charge. 

Since LD sets the A/C in a sealant, to get the old unit off, one must saw the rubber seal in half before trying to lift it.  If you lift first you can stretch the alumimum roof sheet out of shape and it will never be the same.  Knowing this I had brought a suitable saw with me which the young tech used.  Once the A/C unit is removed, the sealant and the bottom half of the old seal scrape right off.  It is like a sheet of plastic putty, not the paralastic LD uses elsewhere on the roof.  The Dometic dealer did not set the new (actually reconditioned) A/C unit in sealant. The dealers hate setting A/C units in sealant because removal is so difficult.

I haven't had a hot day to test the new unit but on a 75 degree day, much like the first trip to the dealer, the new A/C unit produces a 25 to 30 degree split temperature!  Even then the A/C was drawing only 11 amps or so.  We are waiting to see if the new A/C will keep the  coach comfortable on a really hot day.

The temperature measurements are easy to do.  I made them with a Radio Shack automobile inside/outside electronic thermometer.  The current draw measurements are harder.  They were made with a clip-on ammeter in the coach's line cord with all other AC appliances turned off. 

I hope this data will help anyone else having problems with their A/C.   I can't say that anyone did anything wrong in causing this to be such a long process but the situation is not set up to make it easy either.   My dealer was said by Dometic to be much better than average but they still didn't have good skills at diagnosing this problem.  It has certainly taken some time and effort to get this problem resolved.

Linley Gumm                                                                                                                 9/8/02

To make measurements possible I constructed an adapter consisting of a short extension cord that has the outer sheath removed. That way one can close the ammeter's jaws around just the hot, typically black, wire.   My adapter was made out of 15amp hardware store electrical fittings, male on one end, female on the other connected together with a short piece of #12 three wire cord.  I cut away the sheath in the middle of the cord, being very careful not to nick the insulation around the conductors and bent out the black wire so I could clip the ammeter around it.

Linley Gumm                                                                                                                 9/9/02

> I have a 1992 MB and the outer shell of the ac was hit and cracked by  a tree branch. Does anyone have any suggestions as to where I could look to get a new/used one?     Chris