CLARE MEGASAVE M#HEHF-100

[Mickandmousemechanical]

Hey guys,

M#HEHF-100 S#0094052 115v 12A 80,000 BTU High Eff.

I'm stumped.

Came across this 15 year old furnace low boy in a crawl space. Brand new thermostat set for Fan auto, Ambient 22, Set point 27 C. Found the burner cycling. The following are steps I've taken to correct this issue:

1. Cleaned flame sensor and checked HSI (both are fine).
2. Checked amp draw on the V-mtr (rated 3.0A) found 1.2A
3. Went through the safeties and jumped each individually to narrow down the search. All safties are working correctly in the burner circuit. (R.O switch, Air switch, Centrifugal) no High limit switch was found on wiring diagram or on unit.
4. Removed blower panel and tightened belt. (This stopped immediate short cycling and burners run for approx 2-3mins before shutting off and going through the process again).

Found a sequencer rated for H20 C40-120.

My question lies here, is this furnace running correctly (is it supposed to cycle like this)? And if not what am I missing?

:.02: Thanks

[ptemko]

There has to be a high limit. I have never seen a furnace in the age group with out one. It sounds like it is running on limit.

[Mickandmousemechanical]

The only limit I found was the Fan control limit. With the push tab In for manual on and out for automatic (an older honeywell). Is that the high limit? And if so why is it not wired in series with the other limits?

Of coarse there is no manual on site.

[chuckcrj]

What were supply and return temps? Need more info. You can just watch the fan/limit and see if it is tripping or not. Are you a tech?

[Mickandmousemechanical]

Yea 4th year Refrig apprentice G1. Been working in the industry for 6 years. I didn't check the supply and return temperatures. I will need to return, I just need to get more info on this particular unit. What could it be and has anyone seen this sort of behavior from this particular piece of equipment.

[chuckcrj]

It's typical behavior for a furnace that does not have enough airflow. It should not cycle off until the call for heat ends.

[Mickandmousemechanical]

10-4 Will go back and check the A coil. possibly plugged.

[Chris_Worthington]

Thread moved to "Tech to Tech"

[iszell]

Have you tried a CA test

[jetstream]

Also check the secondary heat exchanger, sounds like it could be plugged. Is that the Clare with the secondary ht exch slanted below the filter slot, and the filter slides in horizontally and about waist high?