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  1. #1
    Join Date
    Jun 2003
    Posts
    120
    I have a 3 year old Carrier oil fired furnace Model #58CMA105-12.

    It appears to be a 84,000 BTU burner. Currently it only runs on one speed while the burner is operating and it definitely is a high speed. I have recently noticed that inside the furnace next to the fan is an on-off toggle switch that turns the blower on or off. This switch operates the blower independently of the thermostat.

    I also noticed that when this switch is pressed, the fan runs about 3/4 of the speed of what it does when the thermostat calls for heat. I have also noticed that while the blower is running at this speed and I flip the switch on the thermostat that controls the fan from auto to on, the blower runs at full speed instead of 3/4 speed.

    Inside the furnace their is a diagram with nozzle and pump pressure info amongst other things. I also noticed that there are two rows, one row says fan speed med-hi and the other says fan speed hi. Both have the same nozzle size and BTU rating and both have the same temperature rise numbers.

    Can anyone confirm whether or not this furnace is equipped with a variable speed blower, but the thermostat in the house is a single speed stat and only "calls" for the hi speed?

    any help would be appreciated. I am somewhat handy, could it be as simple as ordering a 2 stage thermostat and installing it?

    If there is information that I have inadvertantly left out, please let me know and I will provide.

    Thanks!

  2. #2
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    Your confusing varible speed with multi-speed blower motor.
    Karst means cave. So, I search for caves.

  3. #3
    Join Date
    Jun 2003
    Posts
    120
    Originally posted by karsthuntr
    Your confusing varible speed with multi-speed blower motor.
    then I meant to say Multi speed. Does this mean that the furnace blower can operate at two different speeds in the heating mode?

  4. #4
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,375
    Originally posted by brewyourown
    Originally posted by karsthuntr
    Your confusing varible speed with multi-speed blower motor.
    then I meant to say Multi speed. Does this mean that the furnace blower can operate at two different speeds in the heating mode?
    No. When the furnace and burner were setup at installation the proper heating speed should have been selected. If you have A/C, cooling usually operates at a different speed. With A/C the thermostat fan switch will turn the blower on at the A/C fan speed. The blower switch in the furnace is for continuos fan operation also. Most people with A/C ignore this as they have the switch on the thermostat.
    Climate Control Solutions for your Home or Office

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  5. #5
    Join Date
    Jun 2003
    Posts
    120
    [QUOTE]Originally posted by comfortdoc
    Originally posted by brewyourown
    Originally posted by karsthuntr
    No. When the furnace and burner were setup at installation the proper heating speed should have been selected. If you have A/C, cooling usually operates at a different speed. With A/C the thermostat fan switch will turn the blower on at the A/C fan speed. The blower switch in the furnace is for continuos fan operation also. Most people with A/C ignore this as they have the switch on the thermostat.
    Why would the furnace run at a lower speed with the toggle switch set to on than it does when the heat comes on? I looked it up on the web and found the marketing flier to this particular furnace which touts it as a multi-speed blower adding to winter heating comfort. What am i missing because I don't want the blower running all the time and when the heat comes on, only one speed goes and that speed is full throttle. There is no multi-speed comfort as described in the marketing flier.

  6. #6
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,375
    What's the temp difference between the supply air and return air as close to the furnace as you can get?
    Climate Control Solutions for your Home or Office

    Serving Northeast Philadelphia and Surrounding Areas

  7. #7
    Join Date
    Jun 2006
    Location
    right, here! in the heartland of the homeland!
    Posts
    737

    I believe

    That although, theres a difference between the multi peeds and uh whatever, theres still a furnace that has or two of them out now that does have that option, i think one is a carrier and a york, and they or some do have dual stage gas valves, some do run on a couple of speeds, who knows read ur homowners manual,
    dont short change yourself, on knowing how your equipment should opperate at its best efficiency,
    When in doubt , Call a contractor out!
    and pay them for their expertise, not just for their time!
    u might have to pull some new wire,and replace the t-stat, too with a dual stage, , let the proffessionals do the work, and learn from them, but dont bother them, let them get the job done, and then ask them what was done or after they finish diagnosing, and not during or before when they finish!
    and im sure you will , be happy, you did!

  8. #8
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,375
    He has an oil furnace.
    Climate Control Solutions for your Home or Office

    Serving Northeast Philadelphia and Surrounding Areas

  9. #9
    Join Date
    Jun 2003
    Posts
    120
    Originally posted by comfortdoc
    What's the temp difference between the supply air and return air as close to the furnace as you can get?
    I'll check it tonight after I dinner, baths and the kids are asleep

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    your furnace has a multispeed blower,the proper speed should have been selcted by the installer based on static pressure (resistance) of the ducts ,or by the "temperature rise" in heating mode.

    Temp. rise is difference between air in and out at the furnace,which is why you were asked that question.

    More air flow less rise and vice-versa.

    Design manual shows rise should be 55 to 85 F .

    [Edited by dash on 12-08-2006 at 04:36 PM]

  11. #11
    Join Date
    Apr 2004
    Posts
    7,680
    I am not going to disagree, the term multi-speed blower tends to imply that the motor will actually use different speeds while operating. However, it is a single speed motor at any given time. The meaning is, that you can have a comfortable (and proper) speed for heating mode, and the proper but different speed available for cooling and these are to be set up by the installer with the correct operation and when it is set up and installed correctly you will be comfortable.

    You were not sold a bill of goods, unless the salesman suggested that you would have some sort of multi speed operation. The "multi speed blower" is a feature, the problem is when someone says this is a feature, they should share with you the benifit, not imply a false one.

    20 years ago, many furnaces had a belt drive motor with an adjustable sheave. I guess using the same logic, one could call them a variable speed blower.

  12. #12
    Join Date
    Jun 2003
    Posts
    120
    Originally posted by comfortdoc
    What's the temp difference between the supply air and return air as close to the furnace as you can get?
    Supply air at closest register is 120 degrees. Return air at the only return I have is 67 degrees.

    Thermostat is set at 68 degrees. Honeywell 3200.

  13. #13
    Join Date
    Jun 2003
    Posts
    120
    Incidentally, to add to my post above. It is currently 23 degrees outside and my oil burner runs about 6 minutes or so every 50 minutes or so to maintain 68 degrees in the house; the blower runs 2 minutes past when the burner shuts off.

    It is a 1200 square foot single story ranch home, 1950's construction with a basement.

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