Unit is around 4 years old and has been a repeat offender with rollout sw trips, soot build-up and sometimes foul smelling exhuast since the second year. Unit belongs to friend who is fed up with the dealer installer due to no resolve. I have disassembled burner,cleaned out soot (alot) from chamber,physically inspected chamber no apperant cracks, checked for correct orfice size,replaced rollout switch with correct replacement (it had cycled so many times it was shot). Reassembled and measured gas pressure 11"wc on outlet of gas valve to burner. Unit flame looks great.my thought now is that this 11" wc is what I should have at the inlet of the vavle and should be actually less on outlet if valve is working correctly? I'm confused can somebody help me or is this unit a lemon?

There should be NO soot formation with a correctly setup and adjusted burner.

Install manual

NOTE !!!

Your LP gas pressure seems to be to high. This might be the reason for the soot. Setting at manifold 3.5 for LP. Read this manual. Page 14 table 6

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/48gp-1si.pdf

Thank you I appreciate your guidance and for the copy of the manual! I will set up manometer again on the valve outlet and see if it will adjust down to 3.5.Will let you know results.

Just follow the manual and it should work.

Did get to unit this week, re-measured valve oulet (manifold) pressure it was still 11" as before,attempted to adjust pressure down wouldn't change at all. The valve is a white rodgers gemini 36g22 type 512 Just looking at the info I have, appears this valve maybe a natural gas only valve ? Maybe getting closer to root cause?

I have not seen any lp units run at 3.5

Joshdta. See page 14 table 6 of the manual above.

Manifold pressure of 3.5 WC on Propane

The manifold pressure is way to high that is why she is sooting up.

This model of Carrier needs a big drop at the manifold if not able to adjust at pressure reg on gas valve might have to change orifices. Turn counter clockwise to lower pressure at manifold. READY 65 you will need a manometer for this job.

This has been a problem in the field since most service people automatically set LP to 11 inches without reading the manual or name plate.

Also see trouble shoot on page 29 table 11 at bottom.

Poor flame. characteristics


Incomplete combustion results in: Aldehyde
odors, carbon monoxide, sooting flame, floating
Flame

Cure


1. Tighten all screws around burner compartments.
2. Cracked heat exchanger. Replace
3. Unit overfired. Reduce input (change orifices
or adjust gas line or manifold pressure).
4. Check burner alignment

Yes it is on lp, but thanks to the kind fellow above I received the install manual and this unit does call for a 3.5"wc on valve outlet even on propane. Orfices are clean and vent fan is working correctly

No wonder it gumed up then. If it has been running like that for 4 yrs, the heat exchanger must about be on its last leg then.

I have one doing the same thing- but it is set properly @ 3.5 wc- for lp gas- carrier sent me a high altitude kit that they say will fix it,basically smaller orfice- cleaned this nasty soot mess up again yesterday and replaced the orfices- time will tell
Anyone else have any sugestions on this- cleaning this exchanger out is a huge mess and hard to know if you have it all out-I use an air compressor and water hose to clean the tubes out

I have a 48GP carrier Unit. I installed a new purge fan and motor, have a brown wire coming off a big blue thing with the other end belong on a pin. Where is the pin for this wire. Yellow wire comes off J1 and also so has a pin ended, where does it go.
Thanks for you assistance'