klixon cra2751-135? where to get, or a close equivalent?

Thread Starter

sdowney717

Joined Jul 18, 2012
705
My heat pump AC runs for about an hour, then the klixon opens.

amp draw through compressor for whole system is 12.5 amps. The fan and water pump draw 2.5 amps
So the compressor steadily draws 10 amps. This is a 120vac compressor.

Can you decipher the klixon code part number? I was thinking the 135 is the temperature it would click off at.
There is a central adjustment with lock nut, can it be adjusted towards the higher temp side, which way to turn, it may be out of spec. This klixon is from 1978 AFAIK.
When it clicks off, the compressor shell is not that hot feeling to me. Maybe moving it a small amount would fix the problem.
1627655774626.png
 

Externet

Joined Nov 29, 2005
1,655
Klixon thermo-switches are abundant and cheap in appliances spare parts stores. Check yellow pages (if still exist) for one hiding by your neighborhood. Also many sites mail-ordering on the web if you supply the AC unit model.
Try re-calibrating it while you seach/wait for the new one.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
Klixon thermo-switches are abundant and cheap in appliances spare parts stores. Check yellow pages (if still exist) for one hiding by your neighborhood. Also many sites mail-ordering on the web if you supply the AC unit model.
Try re-calibrating it while you seach/wait for the new one.
So far I have called 3 HVAC suppliers, and no one has ever heard of this device. Problem is these are sales counter people, and it seems no one fixes anything, but they do want you to buy an entire new AC heat pump.

Other thing I run into is they only sell wholesale.

Do you think a little looser on the adjusting stud will raise the set point? Looser means a little less pressure on the plate, so would take more heat or current to click off? The one I have feels good, not rattling or looking burned.
 

Externet

Joined Nov 29, 2005
1,655
Do not aim for HVAC suppliers; aim for refrigerators, clothes dryer part suppliers !
Stay far away of vendors that do not know about that part. Of course they want to sell new equipment, and the installation, and the warranty, and a monthly fee for checking, and insurance, and whatever they can come up with. Why selling a $5 part if they can go for a $8000+ unit.
Have you tried inserting a piece of cardboard between the heat coupling surfaces once to check if the misbehavior is thermal ? Did you measure temperature ? Did you measure compressor current ?
Can you cool the switch with like a hair dryer at zero heat to confirm it is early thermal acting ? Do you know that a loose/rusty connection to the klixon can heat up its terminals and also its internal guts ? Yes, I would re-calibrate a 1978 switch.

One of many ----> http://www.carbonbrush.com/klixonCRandCS.htm
Similar ----> https://www.ebay.com/itm/1747963820...2FT|ampid:PL_CLK|clp:2047675&epid=11042003109
 
Last edited:

zophas

Joined Jul 16, 2021
113
I think check your water temperature before you adjust the switch and then again after. Many multimeters come with a temp probe. A quarter turn on that nut could give you anything, it might give you 2 degrees it might give you 20. Best be sure.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
can someone look at this info and tell me what is the supposed amperage rating of these two C series klixons?
I found a CRA2736-138 which if the amps were same or higher than my CRA2751-135, I would buy it as it is NOS and cheap

what amp rating for CRA2736
what amp rating for CRA2751
The deciphering type code structure is not making any sense to me for these C series klixon.
scroll to bottom to view amps
Klixon Motor Protectors (carbonbrush.com)

deciphering sheet, I get the C, R, there is no A showing in their code, then these 4 numbers somehow supposed to relate to current. Last 3 digits are terminations.
phen.pdf (carbonbrush.com)
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
Do not aim for HVAC suppliers; aim for refrigerators, clothes dryer part suppliers !
Stay far away of vendors that do not know about that part. Of course they want to sell new equipment, and the installation, and the warranty, and a monthly fee for checking, and insurance, and whatever they can come up with. Why selling a $5 part if they can go for a $8000+ unit.
Have you tried inserting a piece of cardboard between the heat coupling surfaces once to check if the misbehavior is thermal ? Did you measure temperature ? Did you measure compressor current ?
Can you cool the switch with like a hair dryer at zero heat to confirm it is early thermal acting ? Do you know that a loose/rusty connection to the klixon can heat up its terminals and also its internal guts ? Yes, I would re-calibrate a 1978 switch.

One of many ----> http://www.carbonbrush.com/klixonCRandCS.htm
Similar ----> https://www.ebay.com/itm/174796382018?_trkparms=aid=1110018&algo=HOMESPLICE.COMPLISTINGS&ao=1&asc=233150&meid=ea91e10126f34a45a3fe2f5c3afa1f22&pid=101196&rk=1&rkt=12&sd=153320391651&itm=174796382018&pmt=1&noa=0&pg=2047675&algv=ItemStripV101HighAdFeeWithCompV3Ranker&_trksid=p2047675.c101196.m2219&amdata=cksum:174796382018ea91e10126f34a45a3fe2f5c3afa1f22|enc:AQAGAAACAArZmr9qyoSqxkolEiPydiqr8fpVOY%2BwRNZu%2FNxz6xqVKPz9Nq3sc8VSFyPfouZUUZ3bA9sd0Wht4InAzcRq5M46YZ58K%2FEtr7TxaX%2FRGtaXOELHWLycm0FK1CsSvcCrUnb07uebio%2F4JHxSGpN3i%2FHY7RUrSKXj0ZL32iOLD5snNMAe6HVbIe4M982TXqfX7Zv8HRsGlTgtOyK%2BX84um6XWZly1RFXbxdwxtUUmXrlIR5a1L3uT2P0Q5KYyvgeW8rkmG7U4p64NxMrJwk86tmAVieWpVJzCEzGvFmPZL26J8nnY%2F%2FydRZkdkJvJ0WGA76xVB6v8bI2So0pQmFt%2F1kkQlBcT8c%2FRfE9tV8REHI7d9dKps78Xk7SysXCh9i1%2BHB5rCWB66dWbGfiJ4G2M2%2Fe2NejDeNbFA1PAsi%2FBKaNp69nINESnHnXRRQyv85a8y4iO%2BTpY6005v5pEFNUJaBwrNUsV%2Fc5QGddlDRBAD5DAP%2BdsIQrDTTHvGFUlh2kcwjiRycKCjj4%2BbSIldWI5vyEgi0C%2F3hafMYH%2FVrwZvmbVZxUckHurLbG1GdXEaghg%2BBKyNwohLI%2FBn2BLyLtPk1Veo%2Bpt%2B6DvXd81ILerEMCzPqfR6ciqRMc1o4kaU%2B6FfY75mMDqGEISRM5yz3e%2BZzOk4%2B36eINjEduUSAr4lI%2FT|ampid:pL_CLK|clp:2047675&epid=11042003109
it is definitely thermal shutdown by the klixon switch. I ran it till it shut off compressor motor. Measured the klixon and it was open circuit. Amp draw is 10 amps which it has always been, I have a permanent AC volt and amp digital meter on the AC system in the boat.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
I think check your water temperature before you adjust the switch and then again after. Many multimeters come with a temp probe. A quarter turn on that nut could give you anything, it might give you 2 degrees it might give you 20. Best be sure.
yes, I am soaking coil heat exchanger in white vinegar, should clean it on the inside. Then will retry running it.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
I ran a test on Klixon this AM. It can handle amps of 17.6 maybe indefinitely
I bypassed the push breaker and put klixon in circuit.

A toaster that draws 6.6 amps
Heat gun on high that draws 11 amps on high
It also handled 23 amps but I terminated test after 2 minutes (add in toaster other side)

I then pointed heat gun towards klixon and measured temp rose till 221*F where it opened.
5 minutes after pointing heat gun at klixon, it went open circuit.
Total test time, start at 8:16, shut down at 8:25
So it looks like heat load has a bigger effect than amps

I can deduce, the compressor is turning off because it gets warm enough heat after an hour of runtime for the klixon to go open.
Even though warm, my hand feel test on the compressor is not more than 130, I can leave my hand on it barely, right after it shuts off.
So still either klixon is too sensitive to this heat, or the compressor shell gets hotter than it should.

I can try adjusting klixon, move plate away from contacts a bit. But first will see how it works with a vinegar cleaned condenser sea water cooled coil.
1627734822791.png

moved test outside as was heating up kitchen. Amp draw 17.6
Without blasting klixon with hot air, it got barely warmer to touch with just this current flow after 5 minutes
1627735458443.png

Any thoughts on this?
 
Last edited:

Externet

Joined Nov 29, 2005
1,655
Seems it is doing near what it is supposed to.
Added to age of the motor and switch, takes just a few extra degrees contribution by hot summertime to flip the Klixon. Now do the opposite; fit it back where belongs and direct cooling air to it. Also, compressors are meant to work on reduced duty cycle. If running straight one hour, that is another contribution of extra heat.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
Seems it is doing near what it is supposed to.
Added to age of the motor and switch, takes just a few extra degrees contribution by hot summertime to flip the Klixon. Now do the opposite; fit it back where belongs and direct cooling air to it. Also, compressors are meant to work on reduced duty cycle. If running straight one hour, that is another contribution of extra heat.
It may be ok, it could be off just enough to shut off though after a while.
What I dont know is how warm an HVAC compressor shell is allowed to get.
If I had more information, I would know a lot more....

There are alternatives to a klixon. You could use a 15 amp push button breaker. Normal current draw is 12.2 amps according to Tecumseh. Max rated current is 16.5 amps. And for thermal shutdown, use a dryer thermostat, I found one for 155*F. But I am stll wondering about shell temp of a HVAC compressor, what is a normal range, See some of this information HVAC techs will not share with you, as they want you to pay them for a visit.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
On Amazon I saw you can get L120, L130, L140 thermostats.
I may try putting klixon on top of an electric skillet and measure temps to see at what point it clicks off.
 

Externet

Joined Nov 29, 2005
1,655
what is a normal range, See some of this information HVAC techs will not share with you
Highly probably they do not know nor never care. It is much easier to say compressor is bad, is too hot.

If it not published on the compressor manufacturer data/specs, call them to ask. Expect an answer like "70F above ambient"
A HVAC genius does not have the 'tonsills' to investigate. His mission is earn money with the least effort.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
Highly probably they do not know nor never care. It is much easier to say compressor is bad, is too hot.

If it not published on the compressor manufacturer data/specs, call them to ask. Expect an answer like "70F above ambient"
A HVAC genius does not have the 'tonsills' to investigate. His mission is earn money with the least effort.
Hi, I agree. I am at boat and AC has stayed running whole time. Only thing I did was clean sea water condenser with white vinegar. I measured case temp at 155 *F, and have klixon loose under phenolic cover. I will clean again, then recheck on monday. Will show some pics when I get home. With probe under the klixon cover , temp reads 145.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
Current load on the compressor is actully a little low, that tells me the refrigerant level is a little low, which also explains why the compressor is running a little hot and why it turns off. I dont think anything is wrong with the klixon. My plan is to take it down, drain out the mineral oil which I think may be too much in there, suck in some Ester oil, check the vacuum, should be able to pull 20 inches. Tighten all the connections and do a recharge with new refrigerant. But will likely do that later rather than sooner. August starts some cooler weather. I am getting 48 * F at the lower cabin vent, but it ought to be 10 degrees cooler. I actually have a lot of experience with repairing this unit, but always am learning more things. I had this whole compressor condenser apart several years ago.

1627764841558.png

1627765037870.png
 
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It has no run capacitor, or a start cap/relay that is stuck? If so, I would also test those.
Amperage can sometimes be misleading with a motor's power factor, compared to unity like with a heater. So at a light motor load, you can read high amperage but power is low.
But here the compressor's heat is the power meter lol.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
705
All those are ok. It has a potential relay, start and run capacitors. But sure, I will test the capacitance with my meter.
I have in the past had failures of all 3. For example, if start capacitor stays in circuit, it draws ways too many amps and blows the main 20 amp breaker. If either capacitor is bad, it wont run at all. Same with non working potential relay.
 
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