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resqguy · 07-20-2019, 10:08 AM

My refer works fine on LP. When I switch to AC the read out says "no ac". I take the cover off the control board (621271) I see that the F3 is blown. I replace the fuse, plug it back in and it blows again. I looked at some troubleshooting videos and checked some things. The heating elements ohm out to about 59 ohms. Both seem within spec. I replace the control board with a Dinosaur 6212 (set the jumper). When I powered up the refer the F3 blows on the replacement board.

I have removed each external wire and none are shorted to ground or to each other. Any ideas on what to do next?

MSHappyCampers · 07-20-2019, 10:21 AM

Did you check for any reading between the leads of the heating elements and the case? I would disconnect the heating elements and see if it blows the fuse.

resqguy · 07-20-2019, 01:24 PM

I had checked the resistance of each heater element and they within spec ~50 ohms. I also checked each element lead to ground/case and they were open.

I disconnected both of the elements and the fuse didn't blow. I plugged one (lo) in and it was fine. I disconnected it and plugged in the other (hi) and it was fine. I left the refer running for about 10 minutes each time. The refer is starting to get cold.

When I plug them both in the fuse blows, when I just plug in either one - no blow.

Old-Biscuit · 07-20-2019, 02:22 PM

Each element has 2 leads.
1 (yellow) goes on AC-HT-HI or AC-HT- HI-2 (Hot leg)

1 (black) goes on AC-HT-LO or AC-HT-LO-2 (Neutral leg)

F3 Fuse blowing on 2 different circuit boards leaves the heater elements as source of short.

Pappion · 07-20-2019, 04:04 PM

What size fuse are you using? The 5amp or 8 amp.

According to Little-Fuse pdf you should have 25% higher than current draw to prevent nuisance blows.

So 132v / 59 ohm = 2.23 amps for each element. At 50 ohm its 2.64 amps each.

Also GFCI is very sensitive to ground shorts. HOT wire current must be cancelled by Neutral current, within 0.005 amps. To use it for testing plug the frigs AC in to a GFCI protected socket. You can buy GFCI protected extension cords too.

resqguy · 07-20-2019, 05:13 PM

I think I fixed the issue. The whole problem started when my ice maker sprung a leak. I tried to replace the tubing but it became impossible with the refrigeration still in the RV.

I ended up disconnecting the AC from the ice maker water valve and the fuse stopped blowing. Saved the money not replacing the heaters.

Old-Biscuit · 07-20-2019, 05:17 PM

Quote:

Originally Posted by Pappion

What size fuse are you using? The 5amp or 8 amp.

According to Little-Fuse pdf you should have 25% higher than current draw to prevent nuisance blows.

So 132v / 59 ohm = 2.23 amps for each element. At 50 ohm its 2.64 amps each.

Also GFCI is very sensitive to ground shorts. HOT wire current must be cancelled by Neutral current, within 0.005 amps. To use it for testing plug the frigs AC in to a GFCI protected socket. You can buy GFCI protected extension cords too.

OEM Specs for 1200/1201
Each element at 120V
225W --- 1.875A ---64 ohms

2 elements --- 450W 3.75A
5A fuse.......is within 25% spec
(1.25 is 25% ---plus 3.75 = 5A)

1000's of 1200/1201 have used 5A AC Fuse for many years

Dino Board DOES suggest/offer use of 8A with 2 elements

Not sure why the 5A AC Fuse on circuit board would have anything to do with Ice Maker
No wire terminals for Ice Maker on circuit board OEM or Dino

Ice maker either has it's OWN AC Power Cord OR has wire connectors that attach to Ice Maker Wire Harness.

Not powered from circuit board ----Hummmmmm

Pappion · 07-20-2019, 09:40 PM

225W at 120V and 64 ohms is nominal, nominal , nominal. I prefer to plan for worst case.
Generally 132v is used for high voltage alarm or cutoff, by RV power monitors.
Service manual pg15, figure 5, heater resistance range is 58 to 68 ohms each heater, at room temperature. User measured 59 ohms each. OK.

So 132v / 58 ohms is correct by my worst case design. 2 x 2.275 amps = 4.55 amp. 5 amp fuse does not have enough headroom to prevent nuisance blows. Dino board install manual does suggest the 8 amp fuse for dual element heaters.

Oh yea, something is fishy with the wiring. Ice maker should have it's own AC connection, control board etc... BUT early models shared the AC power cord. PG 31.

Old-Biscuit · 07-20-2019, 11:01 PM

Quote:

Originally Posted by Pappion

225W at 120V and 64 ohms is nominal, nominal , nominal. I prefer to plan for worst case.
Generally 132v is used for high voltage alarm or cutoff, by RV power monitors.
Service manual pg15, figure 5, heater resistance range is 58 to 68 ohms each heater, at room temperature. User measured 59 ohms each. OK.

So 132v / 58 ohms is correct by my worst case design. 2 x 2.275 amps = 4.55 amp. 5 amp fuse does not have enough headroom to prevent nuisance blows. Dino board install manual does suggest the 8 amp fuse for dual element heaters.

Oh yea, something is fishy with the wiring. Ice maker should have it's own AC connection, control board etc... BUT early models shared the AC power cord. PG 31.

Shared power cord.....
Means power cord plugged into one outlet then 2 cables plugged into Ice Maker cable harness and Power Cord plugged into circuit board
All that happens BEFORE 5A fuse/AC Circuit on the circuit board
Outlet Circuit Breaker protects the power cord & 5A Fuse ON circuit board protects the AC Detection Circuit and heater elements.
The ice maker and its harness are in no way connected to the refrigerator wire harness, to the power board or to the optical control display assembly.

ANd as posted..........Norcold 5A Fuse is OEM and as been for many years on 1200/1201 models.
Engineers figured it out years ago.
No need to reinvent the wheel

Upping the OPs fuse to 8A does NOT solve the problem
You don't advocate replacing fuses to higher amperage now do you?

Arch Hoagland · 07-20-2019, 11:08 PM

Quote:

Originally Posted by resqguy

I think I fixed the issue. The whole problem started when my ice maker sprung a leak. I tried to replace the tubing but it became impossible with the refrigeration still in the RV.

I ended up disconnecting the AC from the ice maker water valve and the fuse stopped blowing. Saved the money not replacing the heaters.

Thanks for the update.

Old-Biscuit · 07-20-2019, 11:27 PM

Quote:

Originally Posted by resqguy

I think I fixed the issue. The whole problem started when my ice maker sprung a leak. I tried to replace the tubing but it became impossible with the refrigeration still in the RV.

I ended up disconnecting the AC from the ice maker water valve and the fuse stopped blowing. Saved the money not replacing the heaters.

Quote:

Originally Posted by Arch Hoagland

Thanks for the update.

Might have fixed the problem because circuit board/heater leads dried out.

AC to Ice Maker Water Valve is NOT protected by the 5A Fuse on circuit board.

Pappion · 07-21-2019, 06:30 AM

I would never advocate the careless use of larger amperage fuses!

I do have faith in mathematics, my technical knowledge, and research of relevant facts.

And stay within NEC guidelines for wire sizes.

Also, my legal butt is covered. It is Dinosaur 6212 Install Manual that recommends the 8 amp fuse for model with 2 AC heater elements.

https://www.dinosaurelectronics.com/...stallation.pdf

resqguy · 07-21-2019, 09:55 AM

Thanks for the help. I couldn't find a source for the external wiring so the confirmation of the yellow and black wires was great.

I too am confused about the outcome. Since I don't have access to any schematics for the Dinosaur or the OEM board I have to treat these things as black boxes.

All I know is I have a refrigerator that is getting cold and running on AC. Last week was the rebuild of the control wiring of my RVP 6535 basement air. I had a chard control board and three melted caps. The coach in nice and cool now.

Today I hope to get my 7500 generator to run longer than 2 minutes. Then back to work Monday.

Kind of jealous of people getting to take vacations. Hoping to get my turn soon.

Old-Biscuit · 07-21-2019, 12:01 PM

Quote:

Originally Posted by Pappion

I would never advocate the careless use of larger amperage fuses!

I do have faith in mathematics, my technical knowledge, and research of relevant facts.

And stay within NEC guidelines for wire sizes.

Also, my legal butt is covered. It is Dinosaur 6212 Install Manual that recommends the 8 amp fuse for model with 2 AC heater elements.

https://www.dinosaurelectronics.com/...stallation.pdf

Dino replacement board is set up for 5A or 8A AC Fuse BECAUSE that board can be used on several different models of Norcold fridges which is differentiated by the use of 'jumper' in proper slot depending on WHICH Norcold board is being replaced.
(Universal Circuit Board!)

Some OTHER models of Norcold using 2 elements do use 8A OEM
BUT OPs 1201 uses a 5A as OEM spec'd

COurse if OP had mentioned the Ice Maker Water leak in original post we probably would not have gotten sidetracked on 5A/8A Fuse ---this model that model as NONE of it was at issue
Water leaking/fuse blowing-----WET environment ---DUH!

Reinventing the wheel....not necessary