Correct Honeywell limit switch size?

artm

I had a Honeywell limit switch recently replaced on an oil furnace. There's no part number on it but it's about 8-inches long, so I ssume a L4064B2236. The replacement has acted up from day two: getting stuck between off-on, tapping would cause it to jerk, pressing the manual button lightly and releasing back to auto would still run the blower - not always but sometimes.

I looked at my invoice from the oil company and the replacement part is noted as 5-inch, no part number. Well, that's not right I thought so taking out the new part to inspect, it is actually 11.5-inches long, a L4064B2210!

My questions are:

1. Should it act up so soon after installation? Does it need to go through some cycles to "settle in"?

2. Does it matter that the size is different from the old part? Attached are two pics showing the furnace and switch. The switch shown is the old, 8-inch one.

EdTheHeaterMan

Please remove Prices That is one of the rules Here: https://heatinghelp.com/forum-user-manual

Regarding the replacement part. They are adjustable and need to be set by the repairman. If this is a DYI then let me know and I can talk you thru the sequence of operation and how to adjust. It is fairly simple. If this is installed by a contractor, then there should be some degree of warranty the installed should honor and come back at no charge to make it right. At least that would be my companies policy.

artm

Sorry about the price; removed.

I know how to set the limits and I saw the tech do it. The issue is the size (shaft) of the new part compared to the old. Looking at the pic I provided, and where the old part lies in relation to the furnace, can one simply replace the 8-inch with the 11.5-inch and be correct?

HVACNUT

Insertion depth must be OEM specs. If the original was 8 in, then the replacement must be the same.
Describe the problem. What is "acting up"?

EBEBRATT-Ed

I think we all have seen those controls and watched the dial as it "bumps" the don't all work smoothly. Bi metals are a fairly crude control. But I have never seen a new one compleatly and not work.

The length may or may not matter. Call your service company back and have them install the correct control. They can get warranty on the old one

artm

Yes, I described the symptoms above: getting stuck between off-on, tapping would cause it to jerk, pressing the manual button lightly and releasing back to auto would still run the blower - not always but sometimes. Last time it got stuck, the blower was blowing mildly warm air and when tapped the switch jerked to the off position. I can only guess how long the blower would have run if I had not tapped the switch.

This is a 70+ year old furnace (Syncromatic) so knowing what the original should be is not probable. The old switch could have been like the original, if not the original, but it's impossible to know. The size of the old one could be correct. Does it relate to the location of the vent above its tip? That is, should the end of the switch be inside the diameter of the vent above it? The new one, at 11.5 inches long, certainly is NOT.

Lastly, is there another option than using this switch? Something less problematic perhaps?

HVACNUT

Ok, looking at the pic again, the fan/limit was retrofitted in the duct.
Because you're having the same problem with the new control, maybe it's not the control. 
Another option is using a time delay relay for the fan operation and a separate limit, or even a series of limits to open the burner circuit. 

EdTheHeaterMan

I had one experience where i only had an 11" control on the truck and I removed a 5" control. The end or the probe was in contact with the heat exchanger (HX) and I could not get the fan to stop short cycling for 7 to 10 times at the end of the cycle. The HX was so hot that when the fan stopped the probe absorbed the heat from the HX. fan came on and within a few seconds cooled off the probe in 10 seconds. Then back on is 15 seconds... and so on...
In many cases, the length does not matter but in this case, the length did. I was able to make a support, to hold the probe at the correct depth, until I could return with the proper length probe.

In your situation, you may be able to move the lowest temperature adjustment to a warmer temperature so the fan will shut off at a higher plenum temperature. This may cycle up to 2 times after the burner cycles off. That is considered acceptable in older systems. It is just taking that last little bit of heat and putting it in the house. To reduce the number of times the blower comes back on at the end of the burner cycle, you move the middle setting up a few degrees so the fan does not come on so soon.



If that does not solve the problem, then get the 8" model from the repair company.

Getting a time delay to start the fan is another option but do you really want to spend $ on an old furnace. If it is that old, then it may be time to look at something newer and more efficient.

Yours Truly,
Mr.Ed

artm

1. The switch has not been retrofitted. It's in the same position as it was 7 years ago when I purchased the building and it probably was there for many years before.

2. Yes, I am aware that the shaft must not touch anything and the 11.5-inch version does not. Still, I should not expect to see an invoice stating a 5-inch part and an actual 11.5-inch one installed, both different from the original!

3. Yes, this furnace is old - probably as old as I am. I should look into a gas replacement as soon as this heating season is over. I'll start another thread on that.

EdTheHeaterMan

@artm, I was just wondering if you were able to make the small adjustment on the control you have. if so were you able to get a positive result?

artm

Ed, the issue isn't with the settings. It's with the switch randomly getting stuck midway between OFF and ON, requiring a tap to get going again. Plus, the manual control not releasing when the white knob is released.

I have tried the manual knob several times now and it seems to be working correctly. As for the rest of the switch, it still gets stuck.

This symptom, and the fact that the oil guy put in the wrong size (or one different from the existing one), forces me to have them take it out and I'll deal with installing the correct one.

Dave T_2

If you had an 8" and now you have a new 11.5" , the you could pull it out 3.5" and the sensor would be in the same location as the 8" was. If that alone corrects the problem, great, find a way to mount it securely OR simply tell the contractor they installed a 11.5" and you need an 8" like the original - you should expect them not to charge you.
The other thought is the new control may be defective.