Troubleshooting EWC-ST-2D

[Jim59]

Greetings,
I've been having an intermittent zone control problem with the cooling operation of my HVAC system using an Ultrazone EW-ST-2D. All wiring and thermostats are as they have been since the system was first wired and appear to have been correctly wired per your documentation. Essentially zone 2 sometimes cools to a temp several degrees below its set point when both zone 1 and zone 2 are calling. More recently, zone 1 is now sometimes several degrees above its set temp when both zones are calling. To date, I've never had a problem with either zone in heat mode. If I set zone2 off, zone 1 seems to regulate OK.

Referring to the Technical Bulletin for the EWC-ST-2E, and using the checkout procedure (#11 Thermostat Circuit) for the EWC-ST-2E (I can't locate a document for the 2D), I'm getting several voltage measurements in calling/non-calling/off mode that do not agree with the 2E documentation. Essentially I'll get 24V where I should be, but I'm unable to measure any <5V, <6V, <1V where I should be and am generally at ~12V for those points. Admittedly, while in both cases I did not set my thermostat to the temp indicated in that table (Zone 1 was either calling or not calling, while I left Zone 2 off), I figured it didn't matter much as in the cases of all measurements, I was either calling (cooling), not calling (set temp attained) in zone 1, or off (zone 2).

While the system seems to call for cooling OK, I'm wondering if this control board may be smoked and if this may all be related to my zone control problems.

Any and all help GREATLY appreciated! Thanks!

[Eric K.]

Jim,

Please call us while you are home, so we can checkout the system to determine if there is a problem.

Our hours of operation are Monday-Friday 8am-5pm.

Eric