How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Tim H. Your Own Question
Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
Type Your HVAC Question Here...
Tim H. is online now
A new question is answered every 9 seconds

hello, i have a Rheem central heating and cooling unit model

This answer was rated:

hello, i have a Rheem central heating and cooling unit model # XXXXX Serial# XXXXX The unit is over 26 years old. I attempted to turn on the heating system but to no avail. i then replaced the pilot assembly and again to no avail. I think it might be the transformer. I removed the cover where its located and all i hear is a constant humming sound and nothing else. Could this be my my problem? Fan and AC unit work fine.
I will need to gather some more information before I can answer your question(s). Please provide all information I ask for as I am not on site and you, essentially, become my "eyes and ears". In some cases, I may require some readings such as voltage before I can provide you with a satisfactory answer. If you are not equipped to perform these tests, the ability to work through to a solution may not be possible. We always recommend all work be performed by a licensed professional. At the end of our dialog, you will have a chance to rate my service, but please wait until we are done and you have your answer(s).
Hi, I'm Tim and I'm an HVAC expert here to help answer your question(s). Please provide all the information I ask for since I'm not onsite. At the end of our dialog you will be asked to rate my service, but please wait until then and all your question(s) have been answered satisfactorily. Thanks for your business!
Does the fan come on when you turn your thermostat to fan "on" position? If so, this would tend to eliminate the transformer as the cause.
Customer: replied 3 years ago.

yes the blower does turn on when placed on the in position.


OK, let's try this. Turn the power to the unit off. Take your thermostat off the wall exposing the wires and take the red wire off the R terminal and the white wire off the W terminal and twist them together. Then power back up. See if heat comes on.
Customer: replied 3 years ago.

ok please stand by. Nothing happened .



OK, keep me posted.
Customer: replied 3 years ago.

nothing happened.


Ok, is this an electronic ignition?
Customer: replied 3 years ago.

Yes. I replaced the pilot assembly two days ago.


Can you check for voltage at the ignition module across TH and TR? We're looking for 24 volts AC. I'm not sure of the exact model number of ignition control you have and if you could get that to me, that'd be helpful.
Customer: replied 3 years ago.

ok . I have to climb up in to the attic. Please stand by .


OK, sounds good. Keep me posted.
Customer: replied 3 years ago.

Tim are you still with me ?

Yes, I'm here. go ahead. What did you find?
Customer: replied 3 years ago.

First, the panel is a Honeywell 8600F. I found the TH contact but not the TR. I then placed my voltage meter over the contacts and no power to the row of contacts.

OK, since I have no information on this unit and no wiring diagram, please all list the terminals that this Honeywell 8600F has.
Customer: replied 3 years ago.


I did find something on the internet on this. So instead of testing across TH to TR as I previously stated, check for voltage across 24V ground to 24V. This is with the heat turned up or if you still have the red and white wires twisted together, that will work, too.
Customer: replied 3 years ago.

The panel reads: Spark - 24 - 24- Gnd - PV - MV/PV - MV . I placed the red and white wires from the thermostat together then tested the 24 to 24 voltage . I got nothing.

OK, so we need to do a check to see why we are losing voltage to the ignition control. Place one meter lead on the C terminal on the board (if it has one) or on the terminal block where the thermostat wires attach. Place the other lead on the R terminal at the unit. If unit is calling for heat, there should be 24 volts. Now leaving the one meter lead on C, follow the wire that comes off the R terminal and goes to your furnace and it may go to a safety switch or limit control. Test once again for voltage. If nothing there, go to the next spot. And keep going until it gets to the 24V terminal at the ignition control. We need to find out where it's losing voltage.
Sorry, I meant to have you follow the W terminal, not the R terminal. Although you can check for 24 volts across C to R. My mistake!
Customer: replied 3 years ago.

I followed the white wire back to a module with the numbers 222 .


What is this? Do you have voltage here? Can you upload a picture of it? To upload a pic, save it to your PC and using the small icon that looks like a paperclip, upload to the site.
Customer: replied 3 years ago.

Tim sorry for the delay. I'm not so good with computers. I fowarded eight photo's of my heating/ AC unit . I am standing by for your reply. Thanks for your pateints and your help.

OK, did you forward to customer service? By the way, did you have 24 volts across C to R?
Customer: replied 3 years ago.

No power from C to R. I used my cell phone to take the pic's. I then sent them to my email address. From there i fowarded them to your email address. I hope that will work.

If you don't have power across C to R, you either don't have power to your unit or you don't have the blower door switch pushed in. We have to have 24 volts there before anything else will work.
Customer: replied 3 years ago.

could it be a bad door switch? if so how can i check it?

I'm kind of at a loss here since I don't have any information on this unit because of it's age. But yes, if you have a door switch it needs to be pushed in for these tests. If you have a door switch, it should have 2 terminals and you can test from one or the other of these to a good furnace ground and you should have 120 volts. Then when you push it in, you should have 120 volts on both terminals. I know you said you have a blower when you turn thermostat to fan "on" so that tells us that transformer is OK. Do you have a good meter? Is it set to volts AC and not DC?
Customer: replied 3 years ago.

Tim I think I have a bad relay switch. the black wire is connected to the Honeywell (24v) and the white and brown wire are connected to the relay switch. When I connected the white wire from the relay switch and the black wire from the Honeywell 8600F the system fired up. Therefore I am under the impression that the brown relay switch I sent you a pic of is my problem. What do you think ?

I haven't gotten the pictures yet. It will help when I get these and see what you are talking about. Since you said you sent them to my email, I'm not sure where you sent them because my email is not posted. Try sending them [email protected] and have them forward to me.
Customer: replied 3 years ago.

Tim, i'm going to take a chance and replace the relay. its getting cold at night. I'll let you know if that corrected my problem. Thank you again for your help and your pateints

OK,, keep me posted. Yes, good luck! Thanks for using Just Answer and please don't forget to rate my service as that's how we get paid(thanks in advance for any bonus left). Feel free to post back with any additional questions.
Tim H. and other HVAC Specialists are ready to help you