Heat Pump Runs In Test Mode But Not Stat Call - http://www.hvacmechanic.com/ Forums
Original message
| jjnet
 |  "Heat Pump Runs In Test Mode But Not Stat Call"
, posted Tue 8 Jul 13:58  
Trane 3 ton XL19i, 2TWZ9036 two stage, dual compressor heat pump, TWE040 variable speed air handler, Trane residential zoning assembly ZSASSMAL0100, Master Scheduler Thermostat ZUSTATALMS10.
Had fault/defrost light on zone controller board go into a diagnostic indication mode: 10 separate 1-second flashes followed by a single 10 second period of continuous on, repeated ad infinitum. We were told to power system down, wait, then power up again to see if diagnostic cleared.
It did clear, but now we’re not getting any AC. Master controller display briefly shows compressor first stage on, but display goes off after 2 seconds and compressor never actually comes on. Our guy has us on his back burner since we “don’t really need AC at our altitude,” but told us to see if our compressors will run in test mode. They do.
Just out of curiosity, we tried heat pump heat and aux heat as well. Again no compressor action on heat pump heat. Aux heat shows as if on at master stat display but never actually gets powered up.
Our guys have only seen one zoned heat pump in their life (ours). They have no idea what the 10 1 second diagnostic flashes mean, but will “find out from Trane” one of these days. They said something about a possible stuck limit switch, but Trane says it can’t happen.
So what can make the test mode work but not the master stat? Bad stat, bad controller, bad something else? The system has been working flawlessly summer and winter for almost two years including summer highs of 96 and winters down to 15 below. (The heat pump supplies sufficient heat down to about 20 in stage 1 and 10 in stage 2). Any ideas on the 10 1 second flashes?
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Replies:
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| theduke03
| "Re(1):Heat Pump Runs In Test Mode But Not Sta" , posted Tue 8 Jul 22:14
Sounds like your techs are eager to help. If you have a meter, and if you could take pics of the zone panel wiring close enough to read the terminals and post them it would help.
Pics can be uploaded to photobucket.com, click on IMG code to copy it, then paste code in your reply.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Houston204
| "Re(2):Heat Pump Runs In Test Mode But Not Sta" , posted Tue 8 Jul 23:06:
I don't see a ZSASSMAL0100, I only see a ZSASSMAL012.
"Tip of the Day" Remember to remove power first.
[this message was edited by Houston204 on Tue 8 Jul 23:07] |
| | Houston204
| "Re(3):Heat Pump Runs In Test Mode But Not Sta" , posted Wed 9 Jul 00:27
While I don't see it in the installation manual that I downloaded, I'm confident that it is communication failure.
It doesn't look good for your zone control...
Have you had an electrical storm lately? I commonly replace zone controls after storms. (Different brand though)
"Tip of the Day" Remember to remove power first.
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| | theduke03
| "Re(4):Heat Pump Runs In Test Mode But Not Sta" , posted Wed 9 Jul 06:25
No sympathy card to go with the flowers?
"My dad was the most feared furnace fighter in Northern Indiana."
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| | jjnet
| "Re(5):Heat Pump Runs In Test Mode But Not Sta" , posted Wed 9 Jul 14:15
Thanks, Duke and Houston. The Installer's Guide page that Houston put up for the ZSASSMAL012 is almost the same as the relevant page in our manual. It shows all the terminals on the zone controller and how they connect to the heat pump and air handler.
The only difference between ours and the posted page is on the Zoning Config Dip Switch SW1-3: ours says "For factory use set to off" and the posted page says(Off) one & two stage airflow, (on) two step scroll airflow." We keep this switch set to off. Our system was before the XL16i, so we assume the new function of the switch was for that future product.
I finally reached one person (in the country) at Trane willing to look up the diagnostic flash codes for our system. He said the fast flash code we saw simply indicated an error condition in the heat pump. He said it is virtually certain that one of the hi/lo temp/pressure limit switches is stuck in the open position. He's supposed to get back to us today with info on finding, test-jumping and replacing whatever switch is involved. In the meantime we're attempting to locate those switches on the heat pump.
On the power-glitch front it's remotely possible that we had a power problem that might have damaged the zone controller board. We would be happy to pay the $500 for a new card if we had some reason to believe it would fix the problem.
Any help on locating the limit switches would be more than welcome. They are definitely not obvious in the areas currently opened. We see the TXV and its bulb, the defrost card and its coil sensor, the large run and start capacitors and the capacitor switching relay (CSR on Trane's wiring diagram).
Trane's mechanical specifications document for this 3 ton XL19i heat pump (2ZTWZ9036) says:
"Refrigerant Controls: Refrigeration system controls include condenser fan, compressor contactor and high pressure switch. High and low pressure controls are inherent to the compressor. A factory installed liquid line drier is installed."
Is this document telling us that there is no separate low pressure switch? Even Trane doesn't really know the answer to this - at least the Trane people we can actually reach on the phone.
Thanks again for the help.
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| | Houston204
| "Re(6):Heat Pump Runs In Test Mode But Not Sta" , posted Wed 9 Jul 21:12:
If your heatpump runs when you enter test mode, it proves the pressure switch is not at fault.
I don't see a LAT(leaving air temp) sensor on that model, kinda surprising.
"Tip of the Day" Remember to remove power first.
[this message was edited by Houston204 on Wed 9 Jul 21:16] |
| | jjnet
| "Re(7):Heat Pump Runs In Test Mode But Not Sta" , posted Thu 10 Jul 19:35
Houston, there is definitely a discharge air sensor. It's installed on the supply plenum according to Trane's install sheet with its sensor facing away from the strip heat elements but within the main air flow. It connects to contacts T2 and Com on the TB4 connector on the zone controller. This is not shown on the posted page but it is shown on the manual’s following page with the wiring layout and connection diagram.
One of the first things I did was temporarily disconnect this sensor’s wire to the zone controller to see if it made any difference and it didn't. I just now checked the resistance and it was reading 8.45 k-ohms at 82.6 degrees which I believe is in the correct range.
At this point I'm thinking a bad zone controller is going to be the one thing that explains all the pieces of this. The Trane guy I spoke with the other day confirmed that the reason the compressors run in test mode but not in normal mode is that the zone controller ignores fault indications in test mode. So something in the zone controller thinks it’s in fault mode.
Last night I did some quick testing with the test jumper on the defrost board in the heat pump. There's a red wire that can be jumped to either force fault, force defrost, test or normal. When jumped to force fault, the zone controller fault LED flashes exactly as it did when this problem started: 10 one second flashes followed by a continuous on for 10 seconds.
The Trane guy said that this fast flash sequence is a generic indicator for a problem in the heat pump. He felt it was virtually certain that a stuck pressure or temp limit switch in the heat pump would be the problem. But the controller is not showing the fault condition unless I jumper the force fault line. I think the controller itself is stuck in fault mode.
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