Trane RTAA200 low superheat

[DWeddell]

I have an RTAA200 shutting down #1 compressor on code 190, low superheat. I have the manual here and was looking to see what the resistances should be for the suction and superheat sensors. I have ordered a new set of sensors. EXV tests OK with no faults.

Thanks for any advice. I am 99% sure that this is the problem, just want to be 100% sure and want to know what to look for if this doesn't solve the fault 190.

[DVaider]

Hi, DWeddell
The reasons of low superheat in evaporator are wrong settings of TEV (aperture is almost open) and big quantity of ***** in system. If you test your TEV you should wait no less than 20 minutes after starting.

[DWeddell]

Hi, DWeddell
The reasons of low superheat in evaporator are wrong settings of TEV (aperture is almost open) and big quantity of ***** in system. If you test your TEV you should wait no less than 20 minutes after starting.

I see the factory default is 8° F and the TEV is adjustable from 4° to 20°. Perhaps I need to adjust the setpoint. If this is adjustable then perhaps it will tell me if something is wrong with the sensors or not.

I did not have the manual with me yesterday, I left it at home accidentally. Boss was not too happy about that. So I was going to go back later today or tomorrow with the new sensors. Boss also wants me to get a new EXV rebuild kit ($400 US our cost). I just hate to be a parts changer.

[DVaider]

I see the factory default is 8° F and the TEV is adjustable from 4° to 20°. Perhaps I need to adjust the setpoint. If this is adjustable then perhaps it will tell me if something is wrong with the sensors or not.

I did not have the manual with me yesterday, I left it at home accidentally. Boss was not too happy about that. So I was going to go back later today or tomorrow with the new sensors. Boss also wants me to get a new EXV rebuild kit ($400 US our cost). I just hate to be a parts changer.

I understand you - it is so annoying to be only "a parts changer":mad: But you should be careful when you want to change thesettings of TEV, 'cause chiller's "going to conditions" needs lots of time.
Good luck!!!

[DWeddell]

I understand you - it is so annoying to be only "a parts changer":mad: But you should be careful when you want to change thesettings of TEV, 'cause chiller's "going to conditions" needs lots of time.
Good luck!!!

Going tomorrow to replace sensors. I'll post my findings. Thanks for the response.

[Lowrider]

Don't change the SH value!

Did you check to see if the sensors are measering abouth the same as the pipe at the same place?

What did you measure as resistance at what temperature for both sensors?

[DWeddell]

Don't change the SH value!

Did you check to see if the sensors are measering abouth the same as the pipe at the same place?

What did you measure as resistance at what temperature for both sensors?

I haven't checked resistance since I had no value to check. The sensors and a new EXV rebuild kit are both delivered to the job. Was not able to get there today. I'll check and see what the temp is reading against the actual temp when I get there tomorrow. Like I posted earlier, the service manual does not give any values as to what the sensors should read at different temps.

[Lowrider]

No, the iom doesn't, but I have them!!

For some help, the condensation sensor (5R56) is 10k at 25dgrC and NTC.

The airsensor (5R3) , entering and leaving chilled water (5R51 and 5R52, matched pair) evaporator saturated temp and compressor suction temp sensors (5R57 and 5R58, also matched pair) are also 10k at 25dgrC but as noted they are pairs (and different from the other sensor!)

[DWeddell]

OK....Arrived early at 0600 to work on her before cooling demand got too high. 18 ohms at 56F (you do the math). The existing sensors checked out OK. Replaced the m anyway since we had new ones on the job. Placed unit back online and did the same damn thing. Ran fine with 2nd stage locked out, placed 2nd compressor on line and 3 minutes later compressor 1 locks out on low SH. Glad I had the new motor for the EXV. Pumped down and replaced the motor. Placed back on line with both compressors calling and she ran like a champ for about 1 1/2 hours while I tidied up all the wiring and cleaned up my jobsite.

The thing to note here was the dull thudding the EXV made during tests. The board saw the motor responding so it didn't trigger any alert. But, the EXV could not respond quickly enough to changes in the load and I don't think the motor was closing all the way. The new EXV had a nice, crisp clicking during tests by the CPU.

Thanks for all the help and I hope I can help someone else here in the future.

Otto on hvac-talk

[DWeddell]

Also of note is the superheat readings which went as low as 4°F for both compressors. And the new EXV went as low as 50psi which the old one never would do.