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Variable speed scorched air furnaces

M Downey_2
M Downey_2 Member Posts: 21
I was wondering what other wallies thought of the variable speed forced air furnaces ? Are they really worth it ? Seeing that I do exclusively commercial and industrial HVAC (and work for one of the big three manufacturers) I only seem to hear horror stories.  I'd think that the problems with ECM motors have been solved.  I was just planning on installing a V.S. system for one friend, when I hear that another friend was just quoted $1600 for a fan board and squirrel cage replacement on a 3 yr old system.  Wouldn't a 3 yr old residential systems' fan board and squirrel cage still be covered by warranty ? Any insight / thoughts would be appreciated.


  • Tim McElwain
    Tim McElwain Member Posts: 4,556
    What are the problems

    with ECM motors other than failure of the installer to set them up correctly?

    Which furnace got a $1600 quote for a board? Was it an Integrated Fan Control Board or an Electronic Fan Timer board? Did the $1600 include labor? There are now Universal Replacement boards available. The typical furnaces that have the ECM motors are Mod/Con furnaces which are the top end of Forced Warm Air systems. Most problems with adapting an high efficiency furnace to an existing system is that the system is poorly installed and typically has insufficient return air. This presents problems with these type of furnaces.
  • M Downey_2
    M Downey_2 Member Posts: 21
    variable speed furnace woes

    In response to your questions Tim, the furnace is a York Infinity variable speed, natural gas fired. I haven't  been over yet to critique the installation.  I do understand what you're getting at in regards to problems with installs.  I myself have always strived to be the consumate professional in regards to installs I've done, checking gas pressures, temperature rise, duct sizing, etc.  From what I gathered from the homeowner, the service company who responded really wasn't clear as to how much the final price would be.  They also seemed elusive as to whether or not the parts would be covered by warranty.  The tech said something about the board not putting out the full voltage to the blower or the induced draft motor.
  • don_9
    don_9 Member Posts: 395
    Scorched air

    That word should no longer be used with today technology.

    The only way those parts are not under warranty is if the power company has been having problems with their power line running though the area.

    Have to agree with Timmie.i would be checking the static pressure of that system.Some guys assume that if it has a variable speed drive that it can handle a poor distribution system.Its not so.

    Your problem sounds more like a lack of signal from one board to the other or from the stat to the board.

    Happy hunting.
  • M Downey_2
    M Downey_2 Member Posts: 21
    Good news

    I called the local York parts depot and realized that I knew the branch service manager through RSES (Refrigeration Service Engineers Society). I left a message for him to call me which he did promptly. After speaking with me for 2 minutes, he advised me that the problem was the pressure switch.  After replacing the faulty pressure switch, the heat was back on ! The worst part of the whole ordeal was attempting to get the warranty part from York (I don't work for a York dealer) ! Now my buddy has to see about getting his money back from the original service contractor for their obvious misdiagnosis.
  • Slimpickins
    Slimpickins Member Posts: 327
    Pressure switches

    I haven't seen many if any bad pressure switches. Not saying they're not out there and the supplier may have know about a particular bad pressure switch. If you're at altitude, you need a different switch. Before just replacing the switch, you should have tested to see what kind of pressure the inducer is producing. Problem's I've seen with pressure switches are in the venting or a clogged port where the tube attaches to the inducer. The venting may have over the allowed total equivalent feet of piping. The system works when the inducer is new but as the inducer efficiency decreases slighty the pressure switch will drop out after it's running a few minutes. What kind of furnace was it?

    I'm not trying to bust your chops because I know you're helping a friend and he's lucky to have you as a friend. Typically most upper end furnaces with varible speed blowers do have a 5 year warranty. $1600 for a bad diagnosis, wow. At that price i quess they figure they can keep replacing parts till they fix it.
  • Empire_2
    Empire_2 Member Posts: 2,343
    edited December 2009
    Pressure switches?????

    A must in this field is..  1.  U-tube manometer, Even better, Magnehelic, and still better Digital Differential meter and it has to be "0 ed capability.....ZERO.  Pressure switches, either being used as primary or secondary control  or safeties has to be measured and either rulled out ,...or faulty.  Your tool can help you with allot of information.  Let's all of us give a EDUCATED FACT to back up what you see.  Makes the Job go smoother......

    Mike T.
  • M Downey_2
    M Downey_2 Member Posts: 21
    Response re: pressure switch

    Thanks for the input guys, but due to me working out of town at the time, I was unable to actually make the repairs myself.  I just posted what happened so there was a disposition on the post.  After informing my buddy what the service manger said (leading me to believe it's a known manufacturing defect) he contacted a local residential York dealer, who came out and verified that it was in fact the differential pressure switch. Please don't think that I would just swap out the switch without first verifying the actual pressure readings. I carry an inclined tube, slack tube as well as a digital differential manometer on my truck. Unfortunately due to my buddy working midnights and me having to work out of town, there was no way I could pick up parts and make the repairs in a timely manner. One thing that did surprise me was the disparity  between part prices the OEM switch was $7, universal replacement switch (adjustable for actual setting) was $40-50.  Is it really any wonder why they seem to be failing ? :)
  • Tim McElwain
    Tim McElwain Member Posts: 4,556
    M Downey

    who made the Universal Replacement Switch, just curious? Was it from TriDelta?
  • M Downey_2
    M Downey_2 Member Posts: 21
    Pressure switch news from York



    Unitary Products

    5005 York Drive

    Norman, Oklahoma 73069


    Date: February 5, 2009 YS00209


    To: All York Distributors

    All York Branches

    All Field Service Supervisors

    Subject: Pressure Switches PC9, PM9

    We have received several product reports regarding pressure switch problems on the 40”

    modulating 95% furnaces. (Switch P/N S102435308000/

    SAP# 157719 upflow models &


    SAP# 160209 downflow models)

    Investigation into these issues and analysis of field returned switches have shown that the

    fault code 3 is caused by high contact resistance on the electrical contacts within the

    pressure switch. On each ignition cycle, the modulating furnace control ramps the draft

    inducer blower up and down and verifies the pressure sensor and switch operation by

    comparing the switch opening and closing points, as measured by the pressure sensor, to

    the proper switch set point for that furnace model. If the electrical contacts within the

    pressure switch body become contaminated with a foreign material, the switch may close

    mechanically but may not close electrically at the calibrated set point, causing the control

    to detect a pressure switch that is open when it should be closed. This will result in a 3flash

    error code, and the furnace control will not continue the ignition sequence.

    To address this problem, the switch supplier has made a recent change to the switch

    construction to add an industrial contact lubricant that prevents contamination from

    adhering to the electrical contact surfaces. Testing has shown that this makes the contacts

    many times more resistant to contamination by foreign substances. Pressure switches

    with code dates of 0309 (third week of 2009) will have this new construction. Source 1

    should begin to have a limited supply of the new switches available for shipment by

    February 6 th .

    The contact contamination problem will not affect any of the NG33 models, even those

    without the contact lubricant on the pressure switch contacts. The contamination on the

    contacts is usually silicone carbide, the source of which is the silicone hose connected to

    the switch. Silicone molecules outgas from the hose and migrate to the switch contacts,

    eventually affecting the electrical connection. On the NG33 models, which do not have

    closed burner boxes, there is no silicone hose on the side of the pressure switch in which

    the contacts are located, and so there is no direct source for silicone contamination. The

    problem will also not affect previous singlestage

    or twostage

    models, since those

    models do not have pressure sensors that compensate for vent length and firing rate so

    they always provide a pressure level that insures the contacts are cleaned mechanically on

    each cycle.

    This YS letter will provide a replacement pressure switch and one hour labor at the

    dealers registered DOA labor rate. Due to the nature of this issue, we recommend that the

    dealers replace the switches now, instead of waiting for them to fail. Make sure you

    reference the YS letter number when filing claims for this issue.

    For any units in distributor inventory, this YS letter will allow for replacement of the

    pressure switch along with a fair and reasonable allowance. Contact Mark Freund at 4054196609

    for prior authorization to submit the billing for reworking your inventory.

    For repair parts in distributor inventory, contact your Source 1 account representative for

    a Return Authorization of switches with code dates prior to 0309.

    Mark Freund Robert Cabrera

    Mark Freund Robert Cabrera

    Manager, Residential Field Service Director, Indoor Products Engineering
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