timebuilder
12-31-2009, 07:00 PM
LHA120HN1Y
5699B08441
Two stage HP with electric strip heat.
Normally, when I contact the Lennox tech support line, I get first class help. Today, not so much.
Last week, I had my service manager dig out some docs on this unit. Coils were frozen up again, after we had replaced the defrost thermostats a year ago. (After that, the unit behaved normally.)
At any rate, the A55 board had not been responding as desired, and some LED display segments were missing. It was decided I would return with a newer board and install it.
Not wanting to overlook anything, I called Lennox tech support, and was on hold for over 30 minutes. During that time, I started tracing wires, and I found that persons unknown had unplugged wires and reversed them, one wire each from S6 and S9. So, I corrected that and made sure they were right, from the defrost thermostats all the way to the A55 board for the first stage and the HP-1 board for the second stage.
Around that time, the tech support guy answered, and we talked about the board issue and the problem I had seen, and he recommended that I change the IMC. OK.
Because the thermostat is downstairs and difficult to get to, I have heat enabled at the TB-1 strip, to completely mimic the stat. I have my dip switches set, and I restore power. Almost immediately, I see dF2 on the display, and the second stage goes into defrost. Great, I say to myself. The coil cleans up nice and it terminates, and goes back into heating mode. However, all this time, the first stage remained in heating mode. No first stage defrost.
So, I look at the papers that came with the board. It says that if I turn on RECALL and UNIT TEST, and if I press the black button of wisdom for 5 seconds, I can force defrost on for all stages in heating mode. So I do that, and I can see the software version on the LED display, like it also says in the paperwork. No defrost, no matter how long or how many times I press that button.
So, I decide to clear the first stage coil by jumping out Y1, and it cleans up great. Back in heating mode, and the defrost thermostat closes eventually again, and I can read that closure directly by testing the S6 wires on the A55. The drop across the defrost thermostat is a paltry 20 millivolts, so I know I'm showing the A55 that the coil is ready to defrost. No joy.
When I still had the tech support guy on the line, he had no idea why the unit would not defrost the first stage, even after the 32 minutes of run time I had programmed into the ETCO.
So, can any of you Lennox guys suggest why the second stage goes into defrost splendidly, and the first stage will not?
5699B08441
Two stage HP with electric strip heat.
Normally, when I contact the Lennox tech support line, I get first class help. Today, not so much.
Last week, I had my service manager dig out some docs on this unit. Coils were frozen up again, after we had replaced the defrost thermostats a year ago. (After that, the unit behaved normally.)
At any rate, the A55 board had not been responding as desired, and some LED display segments were missing. It was decided I would return with a newer board and install it.
Not wanting to overlook anything, I called Lennox tech support, and was on hold for over 30 minutes. During that time, I started tracing wires, and I found that persons unknown had unplugged wires and reversed them, one wire each from S6 and S9. So, I corrected that and made sure they were right, from the defrost thermostats all the way to the A55 board for the first stage and the HP-1 board for the second stage.
Around that time, the tech support guy answered, and we talked about the board issue and the problem I had seen, and he recommended that I change the IMC. OK.
Because the thermostat is downstairs and difficult to get to, I have heat enabled at the TB-1 strip, to completely mimic the stat. I have my dip switches set, and I restore power. Almost immediately, I see dF2 on the display, and the second stage goes into defrost. Great, I say to myself. The coil cleans up nice and it terminates, and goes back into heating mode. However, all this time, the first stage remained in heating mode. No first stage defrost.
So, I look at the papers that came with the board. It says that if I turn on RECALL and UNIT TEST, and if I press the black button of wisdom for 5 seconds, I can force defrost on for all stages in heating mode. So I do that, and I can see the software version on the LED display, like it also says in the paperwork. No defrost, no matter how long or how many times I press that button.
So, I decide to clear the first stage coil by jumping out Y1, and it cleans up great. Back in heating mode, and the defrost thermostat closes eventually again, and I can read that closure directly by testing the S6 wires on the A55. The drop across the defrost thermostat is a paltry 20 millivolts, so I know I'm showing the A55 that the coil is ready to defrost. No joy.
When I still had the tech support guy on the line, he had no idea why the unit would not defrost the first stage, even after the 32 minutes of run time I had programmed into the ETCO.
So, can any of you Lennox guys suggest why the second stage goes into defrost splendidly, and the first stage will not?