heat anticaptor failure

JackEnnisMartin

More years back than I care to mention I ran into a problem I had never had before. We had installed two relatively large heat cool Carrier units on the roof of the Old Sphageti Factory, a restaurant in Winnipeg Manitoba.The units replaced Hastings duct heaters and were fired at 550,000 btus each. The units came from Carrier specified to have one and one half horsepower three phase motors given the size and the static for the duct work. We started the units and on came the problems. I was then a young jouneyman and it feel to me to repair what was wrong. The space [ Brandy's Bar ] would not heat and nothing we did would bring the space up to temperature. I traced out the duct work [ I hope the installer did one more job and then sold shoes] and found it to be too small for the cfm it had to handle to supply the requirements of the bar. Time after time I went on calls no ventialtion etc. I tried to talk to my boss about the duct work but; he would not entertain the idea the "expert" who sized and installed it could have made a mistake! Finally one night I was called to the bar for the umtenth time and I finally found the cause or evidence what was happening. I took the cover off one of the Carrier stats and the heat anticapator spring was so wound out that it was at least four times it's proper size-- in effect the stat was ruined. What was happening turned out to be so simple[ most of them are] the units were going off on the high limit so often because the motors could not push the fan fast enough to provide enough air to keep the air temperature in the correct operating range.Of course, in such a case, the anticaptor on the stat is still recieving voltage for early unit shutdown and use of the residual heat to bring the space to the set point temperature as it was designed to do. Armed with the stat I marched into my bosses office and showed him what incorrect sizing of duct work can lead to. He finally agreed and we installed three horse power motors and had the shivs on the fans changed to bring the max. air possible across the heat exchangers of the units. The space went to design temperature and ventilation percentage. It is the only time I have ever seen this happen and to this day I am still shaking my head -- why be ignorant of your chosen profession -- in this case sheetmetal when there are so many excellent books and courses avialable to enlighten your leve of expertise? The units were excellent pieces of equipment and Carrier was not to blame in any way for this mess. Hope it helps someone else in the future.