My true blue 90 Quatro furnace had a pressure switch replaced yesterday. (Consolidated industries USA 072 NH3R) After it was replaced, it would only fire with the door off the upper combustion area. The technician started checking for blockages in the exhaust and intake air. Funny thing, they found no blockages in either, but after they had cut into the exhaust line the sealed it back, the furnace wouldn't ignite even with the door off the combustion area. They are supposed to return today, but said they needed to research the problem. Could the problem be the heat exchanger? Are there any other small sensors or dirt issues that could cause this problem? Thanks for any answers. They were talking replacement furnace when they left...

What was the reason for replacing the pressure switch? Was the unit working before the part was replaced? Are you certain the correct replacement part was installed? Jeez, you were seeking answers and all I gave you was more questions... :D

I hope this is the correct place to reply. The unit would work, but it was cycling on this making kind of a clunk, clunk trying to start up. It would start, but it took many tries. First technician looked at it and said it was the pressure switch. He couldn't get the part, so the other company said they could. They ordered and installed the part based on the first technicians advice.

Post the complete model # of the furnace if possible. Do you still have the original pressure switch?

Yes we do. The model of the furnace is USA 072 NH3R.

I'm not finding much online info for your furnace. Look for a spec label on the old & new pressure switches. See if you can find the operating value of either/both. May look like '0.35" WC'.

Thanks for your help. I'm not sure about the operating value. I had another technician come out and look at the unit yesteday evening. He said the ignition fine, gas flow fine, he thinks the secondary heat exchanger is clogged. The unit will run as long as the cover is off the combustion box. It will not cycle back on after running. The tech says he can open it and try to clean it, but it would be impossible to get another heat exchanger for this unit. He explained that it is possible that when trying to clean the heat exchanger it might fall apart due to rust and deterioration. He also said replacing the black motor on the front (called an inducer I think) , it would cost maybe $300, a lot to pay for something that may not solve the problem, if the secondary heat exchanger is clogged. His company can install a GMV 95 Goodman for $2800, or a Trane for $3500. The other company had mentioned an American Standard for $3500. Now we're just trying to figure out what is the best. We give up and now think that trying to repair a unit that is almost obsolete is just throwing good money after bad.

Probably a good decission to replace. The quatro was built by consolidated and now out of business. The Goodman if installed properly will do a good job.

Thanks for the input.