Coleman MACH AC unit acting up!

[ClydesdaleKevin]

So the front air conditioner unit on our 1995 Itasca Suncruiser is acting up.


It is a Coleman Mach series, and is the original one on the coach.  It is a ducted unit.


So here are the symptoms:  When it reaches the set temperature on the wall thermostat, the fan shuts down, but the compressor keeps humming and doesn't shut off like it always has before.  And now the cooling fins freeze up into a block of ice (the fins you can see from the inside if you take the ceiling vent cover off).  When the fins freeze up, air flow obviously stops, and it stops blowing cold air, even though the compressor and the fans are still working.


So now I have to run the rear AC until the front AC thaws out completely...and then I can turn on the front AC and it will work for a whole day...and then be frozen again by morning.


It is stupid hot and humid right now in south central Georgia.


I have the means to buy a new one, but don't want to shell out almost a grand if I don't have to.


So any thoughts?  Are the symptoms familiar to anyone here?  What would cause the compressor to keep running even when the fan shuts off?  If I shut off the wall thermostat, the compressor STILL keeps running, until I hit the hard switch that turns the AC on from the front to the back.


Is there a relay up in the top unit that might be sticking open?  Would a bad capacitor do this?  Am I looking at an easy fix, or a replacement?


Thanks!


Kev

[Rickf1985]

It sounds like the compressor relay is sticking on. This could be very bad for the compressor since it will eventually start getting liquid back to the inlet of the compressor. I am not real familiar with the circuitry on this but I would guess there is a timer for the circuit that shuts off the compressor first and then the fan a couple minutes after. That is the usual setup. Since your fan is shutting off it sounds like the compressor relay failed to drop out. The compressor is a high load item and should have a relay somewhere. The capacitors failing would prevent the compressor or fans from coming on.

[ClydesdaleKevin]

So I called Camping World, and they were no help, even though I gave them the exact model of AC unit we have, a Coleman SuperMach 6799-807. Coleman is closed for the weekend, so back up on the roof I went! I removed the shroud and the plate that holds the capacitors, and thankfully all three (yes, there are three of them on our unit) were still legible on the sides. So I ordered three new capacitors with the exact same specs from Amazon, and they should be here in a couple of days. I also ordered a Coleman AC relay from Amazon that should be here in less than a week. The relay wasn't marked, so I guessed a bit...an exact replacement with the exact positions of the terminals wasn't something I could find, but this one does say Coleman, etc, and the terminals are numbered the same. Hopefully it is just one or more capacitor, which I will replace as soon as all three get here. They were cheap. If that fixes it, I'll return the 30.00 relay and get my money back...or use it if I have to. I'll let you all know if it fixes the problem!

Kev

[Froggy1936]

Kev i doubt that any capacitor could cause that problem , They are only used for increased power on compressor start up esp under load, Sounds more like a relay or possibly thermostat if it has fan only capability.   Frank

[ClydesdaleKevin]

So here is a little update on the air conditioner.


I'm still waiting for the capacitors and the relay to arrive...but for now it seems to be working just fine again.  When I went to get the part numbers off the capacitors and relay, the relay was covered with old mud dauber nests...so I had to tap on the nests and break/scrape them off.  And I think that freed up the relay.  Either that, or there was a bad wire connection, and removing/reinstalling the wires on everything corrected the problem.  I'm going to leave well enough alone and just keep the parts as spares and use them if I need them...but for now?  If it ain't broke, don't fix it.


I also managed to install a new and proper 30 amp power cord and outlet and outlet box to plug the coach into, since the previous owner simply buried an RV extension cord to get power to the coach.  So now the RV is on a good power source with a brand new breaker.  Because that other cord was there on its own breaker, I decided to run a cable from the generator compartment and tie it in to the cable that goes into the coach to power the rear air conditioner when the generator is running...and put a 30 amp plug end on the other side, plugging it into the old plug coming out of the ground.  So now I can also run the rear AC on really hot days, and it is running off its own breaker!  SWEET!!!


And I also designed and hooked up a hard PVC sewer line to the coach which works perfectly and eliminated the fly problem we were getting around our flexible sewer hoses...apparently flies can smell right through those thin flexible hoses.


I'll post some pictures when I get a chance.


Kev

[Oz]

Cool, Kev.  Let us know about your new parts and if the unit continues to work!

[ClydesdaleKevin]

Cool, Kev.  Let us know about your new parts and if the unit continues to work!

Will do!

Kev