I'm a hvac certified tech and am working on Carrier 40gc900220, around 30 to 40 years old, been told even the model number is obsolete. My top 5 kilowatt heat strip is getting no power but has continuity and 14 omhs resistence. My bottom strip has power and has a loop the goes up and connects to the top burner on the right side. The left terminal on the top burner connects to the NO side of a relay switch. The relay switch is a spst . When I test this relay when there is a call for heat, I get 24 volts across the contacts. Doesn't that mean that the switch is bad and won't let current pass thru? Or just that when it's energized that it opens to allow NO to close? Also, the NO open contacts are 240 volts for heat strip and second relay, when I test across these terminals on a call for heat there is no power, doesn't this mean the switch is open and fucntioning properly? Also there is a control switch of some sort that feeds the 2 switch relays...is has a post marked COM and one marked NO and 2 marked HEATER. They are not inline, parallel, etc. Would you test this switch for continuity with one lead on COM and one on NO, or one on COM and one to the heater leads in turn? Another words, which is the load and which is the switch?

NorthernHeat

To many questions, I lost track. So the #1 heat bank tests good on continuity and has not got 240 V across it? This relay uses 24 V to switch a 24 V circuit for heat? Can you hear the relay close? Do you get continuity across it with 1 wire removed and it is energized?

hvac1000

Have an expert in HVAC rewire the unit to use a Sequencer. Just did one the other day. Any HVAC tech that has been around can do that for you an eliminate the old Carrier relays.