Roof top AC

[Lin]

I just bought an old, cheap Dodge motorhome to use a little guest room or storage.  The rooftop AC fan works but the compressor does not kick on.  I tested the continuity on the thermostat and it appears that there is none, so I thought that was the problem.  But when I jumped the two wires, there was just plain no reaction-- no buzz, no spark, nothing.  The hot wire was hot.  Am I right in assuming that connecting those two wires should turn the compressor on, or is there something else to do?  Are there generally any internal fuses for the compressor in these.  Although I did not find any manufacturer info, it looks like a Dometic to me.

[Blacksheep]

Sounds like a bad capacitor. It might have two. A start cap and a run cap! I'm sure Nick or someone will correct me when they see this as I'm really only going on memory and from what I have read!

Ace

[Nick Badame Refrig/ACC]

Hi Lin,

Ace is correct but, current first flows through the selector switch before the t-stat. The selector must be in the cool setting.

With any electrical problem, start at the source and work your way to the final destination. Yu'll get it!

Try those first and let us know where you are at.

Nick-

[Lin]

Yes, when the function switch is one cooling, the fan continues to run and the black wire to the t-stat gets current.  There is a brownish wire on the other spade of the t-stat.  I disconnected both wires and held them together and nothing happened.  I guess the next step is to take off the shroud and go for the next component.  How do I test the capacitors?

[JohnEd]

Lin,

I have a Coleman from 1974 that had power applied for the first time today....it runs fine and puts out cold air.  Don't tell it how old it is.  I have two Dometic "Quick Cool" units that I will test on Monday and a Dometic Low Profile that I will also test.  Should we talk?  I wish you well with your test and hope that it is only a cap or wire that came loose.

John

[Lin]

John,
     I will let you know what happens.  I am hoping that it is fixable.  The t-stat started to work.  I guess it just needed some exercise.  Unfortunately, the compressor still does not turn on.  I will dig deeper during the week.  Do you know how to test a capacitor?

[Len Silva]

You do know that there is a delay in the compressor starting, could be a couple of minutes.

[Sojourner]

I just bought an old, cheap Dodge motorhome to use a little guest room or storage.  The rooftop AC fan works but the compressor does not kick on.  I tested the continuity on the thermostat and it appears that there is none, so I thought that was the problem.  But when I jumped the two wires, there was just plain no reaction-- no buzz, no spark, nothing.  The hot wire was hot.  Am I right in assuming that connecting those two wires should turn the compressor on, or is there something else to do?  Are there generally any internal fuses for the compressor in these.  Although I did not find any manufacturer info, it looks like a Dometic to me.

Before you buy a capacitor...do the following steps.

About no-nothing sound after connecting stats wire. I assume that blower work but no humming sound from compressor. Which means either the compressor's relay in control box is dirty contact...replace or compressor's over-load circuit breaker (inside of sealed unit) is sucked open.....you exchange compressor (Hope it not this).

About capacitor....it only bad when compressor is humming & getting hot but not running or pumping after the stat turn on power. In other words, it will pop the power breaker while energize 30 seconds or more. It only use for starting electric motor...not for continuous running.

However, if no blower & no compressor & no humming....check the stat's wiring for broken circuit or check for 12 volts power to the A/C unit as well between the stat's wires.

What make & model?

FWIW

Sojourn for Christ, Gerald

[Lin]

Well, I let it run for a while and it did start.  Maybe it is as Len suggested that there is a time delay built in.  I have two Coleman units in the bus, two Dometics in the last bus, and another in a past motorhome.  I do not remember any of them having such a substantial delay.  I also had let this one run for a few minutes yesterday and it did not start.  Anyway, I would rather have this as a false alarm rather than have to fix or replace it.  It would be nice if all problems fixed themselves-- maybe. Thanks for the help.

[JohnEd]

Lin,

Not to rain on your parade, but... all of my colemans start the compressor as soon as the thermostat clicks.  I start off at a high temp with the fan on high and lower the thermostat temp and when it clicks the compressor kicks in and cooling we go.  Haven't done the Dometics yet.

Best wishes to you Buddy,

John

[Nick Badame Refrig/ACC]

Lin,

Not to rain on your parade, but... all of my colemans start the compressor as soon as the thermostat clicks.  I start off at a high temp with the fan on high and lower the thermostat temp and when it clicks the compressor kicks in and cooling we go.  Haven't done the Dometics yet.

Best wishes to you Buddy,

John

Hi John,

Lin's unit most likely has weak start windings in the compressor. He may not of heard the compressor trying to start a few
times before it finally turned over.

Just a scenario
Nick-

[Lin]

Nick,
     I will not discount any possibility, but I really listened for even the slightest acknowledgment when turning the handle to "Cool".  I know also that I kept turning the t-stat up and down and did not get the characteristic click.  Further, there was no continuity at even the coolest setting.  This morning I was in the motorhome doing something else when for no reason, it clicked.  Since I thought I recognized the sound, I tested it.  Not only did it click on and off, there was continuity.  A bit later, I figured I'd place another bet, turned the unit on and sat down for a while.  It may have been several minutes, but it kicked on.  I thought that I should have gone to Vegas this weekend.  I do not know what will be with it tomorrow.  I think that it was just shy and was waiting to get to know me a little before playing.  We'll see what happens come spring.  It was in the 60's today at best.

John,
     My Colemans start right up too.  I think my past Dometics did also.  I won't swear to it though.  But this one, if original, is from 1973.  If it has a delay, even if it is a freak, I'll still be happy if it works.

     It's funny how things work.  Some guy was getting rid of this motorhome and dropped his price to $400.  I thought, "Well I've got all sorts of people coming for Thanksgiving.  I'll buy it, clean it up and someone can use it rather than stay at a hotel."  I figured I could always resell it later.  It was not supposed to be a project, but I'm already spending time on it.  The only reason I want it to run is so I can move it around my property.  It will not even be road registered.  Yet today I pulled the water pump because it plans to disintegrate the next time I try to move it 100 yards.  I hope it will leave me only after that.