Carrier 58MXA pressure/vacuum problem

gshock

I've got a Carrier Weathermaker 9200 (58MXA), and it fails to start every once in a while, giving me the " 3 -1" indicator lights. This has happened before, and it was thought to be a loose connection on the pressure switch. While troubleshooting, I've found that if I squeeze the vacuum tubes, the furnace will start up normally, run for several weeks or a month, and then fail to start. In an earlier post, someone commented that problems with the vacuum lines indicates a much bigger problem. Is it that, or could it just be a bad pressure switch? Could these lines become clogged for some reason? Can I blow compressed air to clean out the other end? I'll take it all apart myself, but I don't want to have it down for more than half a day as winter has settled into my neck of the woods ... snow and all!

TIA

#CARRIERMAN

Hi gshock

It could just be the pressure switch is bad. Here are some things that will help you determine this. Does it happen the same time approximately every time. Does it only do this when the temperature falls drastically. If you answered yes to these first two, you are having a pressure problem in the heat exchanger. This could be due to a plugged condensate drain or algae build up in the heat exchanger. If you answered no to these two questions, get you a pressure switch and install. The pressure switch for this furnace when I quit doing this was about $40.00. They could have gone up in the last year though.

Good luck
Rusty

__________________
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gshock

#CARRIERMAN,
Thanks for the tips. The answers to your questions are "YES." Typically, it fails to start about the same time each time, and it's typically coupled with big temperature drops. Also, the humidistat was set by the previous owner to a very high humidity level. I suspect that's contributing to the problem. We were getting a lot of condensation on the windows and turned it back down ... almost down to zero.

So what's the best way to clean out the algae if there is any? The technician did clean out a clogged condensate drain the last time, but I don't think he did a good job. The Mrs. tells me he just blew threw it. Talk about hi-tech. I was at work so I didn't see what he did.

TIA.

p.s. already bought a replacement pressure switch, but I'll wait to see what you suggest before replacing it.

Cheers.

gshock

I made a new post, and was wondering if you can help me out.
http://www.diychatroom.com/showthread.php?t=14324

Originally, I answered yes to both questions. More recently, in the last two months, the answers to both questions have been, "No." The furnace is quiting at all times of day or night, and it happens when temps are consistent. I have a pressure switch and will replace tonight. Could it be something else?

dbp

I have the same symptoms. Seems to happen intermitently, but roughly in the late afternoon and also when the temperature drops frequently. Did you ever discover the solution. My HVAC guy can't figure it out.

gshock

Yeah, i just replaced the pressure switch and it works fine. It's been humming right along for over a month now. I haven't had a single hiccup since I replaced the pressure switch. It's only a $40 part, and far cheaper than having a repair man come out. It's a snap to do. Before you disconnect anything, get the new Pressure Switch, and move the lines, wires over one at a time. Helps to avoid mistakes. Then you just have to swap the part. There's a machine screw holding the old one on.

bigMikeB

I hope you used an exact replacement pressure switch. Some have adjustable settings and the wrong set up could be very very bad.

gshock

yes, it was a carrier replacement part. The original was replaced by a different part number, so when you look for it, you find a "replaced by" part number. Based on how the vacuum tubes hook up to it, I can see why they changed it. The old part stretched the tubes too much and caused them to crimp. This new one lets the tubes bend more freely. It's been working great so far, and we've had some VERY cold nights.

bigMikeB

Glad to hear it worked out right.