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Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 10334
Experience:  RVDA/RVIA Master Certified Technician with many years experience.
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I have a 2009 Dutchman Super C Rv with two AC units. The

Customer Question

I have a 2009 Dutchman Super C Rv with two AC units. The unit in the rear or bedroom is blowing the fuse on the Mach 3 thermostat. The AC unit is Coleman Model #8333D8764 no heat just AC. If I by pass the thermostat and put the 12v hot and the fan wire
and the compressor wires together it runs fine. If I jump the fuse it will burn up the thermostat. The fan will come on but not the fan and cool. Just wanted your thoughts before I replace the thermostat again.
Submitted: 1 year ago.
Category: RV
Expert:  Randall replied 1 year ago.

Do you have a small digital multimeter so you can take some DC voltage readings? Have you had the batteries serviced recently and how old are they? Make and model of your converter or load center? Get back to me with this information and I can assist you further. R.J.

Customer: replied 1 year ago.
on the meter. The batteries are about a 1.5 years old. I am not serviced them. There is two batteries. There is two converters. The one that plugs into the back of the 120v panel and feeds the 12v panel is a WFCO 55amp model WF-9855
Expert:  Randall replied 1 year ago.
Two converters? Please explain. And what kind of DC voltage to you read AT the fuse on the thermostat? You will have to find a good ground to use. Also what kind of DC voltage do you have coming TO the batteries? Check the water level in them and see if they are "dry" or can you see fluid? Let me know what you find.
Customer: replied 1 year ago.
I believe the second converter runs the tv system. The voltage at the fuse is 12volts
Expert:  Randall replied 1 year ago.

And when you jumped the fuse you toasted the thermostat? What about the batteries?

Customer: replied 1 year ago.
The batteries are good. The rest of the rig works fine. The other AC frig lights are all good. The other converter is a inverter. World Friendship Company model WF-600 TH-112 (W/AC pass through switch and remote.
Customer: replied 1 year ago.
I believe that inverter keeps batteries charge when plugged in to shore power.
Expert:  Randall replied 1 year ago.

And did the thermostat get fried when you jumped the fuse?

Customer: replied 1 year ago.
it fired. The fan only function would work but not the cool with fan.
Expert:  Randall replied 1 year ago.

Then from what you have told me, it would appear that there is a problem with the compressor relay and that is causing the fuse to blow and if you bypass this then it will burn up the thermostat. That needs to be tested. It may be a problem with the compressor itself. Testing would show what the condition is. That would take a tech with the knowledge of this system. Hope that proves helpful here. Please get back to me if you need more as all follow ups are included in our fee.

Customer: replied 1 year ago.
The system will run fine if I put the 12volt hot together will the fan high or low speed and the cool wire. I don't think the compressor it's self was a problem it was ran that way for the last week. Can you tell me the part number for the compressor relay for that unit?
Expert:  Randall replied 1 year ago.

Sorry..........I forgot that you told me that. Long day! So if it works that way it would appear that the thermostat just gave out at that point and replacing it would solve this. You might be able to upgrade to a newer version as well. Thanks for giving me a good description of the things you tried.

Expert:  Randall replied 1 year ago.

I am trying to fully understand what was said before.........did you replace the thermostat already? IF SO, was it the same model or a different one? IF it wasn't the same, it may not be compatible with your system. There should be a part number on it once you take the cover off. R.J.

Customer: replied 1 year ago.
I have replaced it twice. It has been with the Coleman Mach 3 both times.
Expert:  Randall replied 1 year ago.

There are a number of thermostats that have the same PLUG(s) on them, but they aren't compatible with every Mach 3 model as they have made numerous variations of this A/C. Did you keep the OEM part you replaced? See the link below for a list of the current thermostats. Take the covers off the ones you have and check the part numbers. Give them to me and the OEM if you still have it? http://www.rvcomfort.com/rvp/pdf_documents/2013_tstat_catalog_upload.pdf

Customer: replied 1 year ago.
The first time I replace it it work for about 6 trips. Then it blow the fuse. I was out in the middle of no where and by passed the fuse and it ran for another 4 trips bypassed. Then it fried the thermostat. So I replaced the thermostat with the new one and it ran for about 2 trips and blow the fuse and when I by passed it that time it fried the thermostat right away. So I wired it direct and it ran for a whole week no problems. But now I want to get to the bottom of this before I burn down the whole thing. I believe it is the compressor relay. The fact that is was hit and miss in the beginning and now it blows fuse right away now. What is the part number for the relay?
Customer: replied 1 year ago.
Shit you might be right on the thermostat. I don't have the OEM one anymore it was last year when it went out. I went to a RV store and look for the same one and the told me that this one would work. I remember the OEM one only had cool no heat and then a fan high or low and auto. You think that will make a difference? Can you tell witch is the right thermostat for my unit?
Expert:  Randall replied 1 year ago.

This version doesn't use a compressor relay. So, I would look for a chaffed wire harness that would cause a short sometimes. That makes more sense from what you just shared. See the link here showing the parts for this model. Check this and get back to me tomorrow. I am calling it a day as it is late here and I have to get up early to get to my "day job".............thanks for hanging in there on this! R.J. http://www.rvcomfort.com/rvp/pdf_documents/r524.pdf

Expert:  Randall replied 1 year ago.

I would have to make a call tomorrow and find out which one from the list is the correct version. I will get back to you early tomorrow.

Customer: replied 1 year ago.
Did you forget about me?
Expert:  Randall replied 1 year ago.
No........just took some time for them to call me back. The basic thermostat that should work on that A/C is a part number 7330G3351. Take the cover off and give me the part numbers of the ones you got. IF they are digital, I will need to call in again. That one I gave you is a basic slide control version. R.J.