HVAC Tech Help?

[SS MAYFLOAT]

I've had some problems with an old YORK commercial 10 ton unit. A professional outfit worked on it for 5 days and never got it running. He stripped out an old relay board (Known to go bad & obsolete). He didn't bother unhooking other componets like the equalizer that hasn't worked in years. Unit is over 20 years old.

I did get the unit wired and going,,,however one night it almost caught on fire. The Hi=limit did shut the unit down. I don't know if someone accidently changed the blower setting on the stat or if the blower just quit and caused the unit to overheat.

For the sake of safety, should I install a sail switch on the intake of the evap blower? This way if the fan fails for any reason it will open the circuit to the heat controls.

I'm going to check to see what the temp range on the Hi=limit is. I'm thinking maybe some other tech from previous repairs may have put in too high of a spec on the Hi-limit. This unit got so hot that the plastic cover on an old W7400 module melted. That was another part that was bypassed and never removed fromt he unit as well. It is out of there now.

The unit ran for 18 hours without any problems until it overheated. The heat exchanger was replaced last season, but I'm going to see if it prematurely cracked. Might be why the unit overheated as well. That is why I'm thinking that a sail switch would add another safety feature. What do you think?.......SS

 

[dolluper]

Re: HVAC Tech Help?

Think you nailed it on the high limit....blower wiring is ok?

 

[SS MAYFLOAT]

Re: HVAC Tech Help?

Think you nailed it on the high limit....blower wiring is ok?

Yep, the wiring on the blower is correct. It is 208 3ph controlled by a 3 pole contactor. The coil on the contactor is 110volt which is controlled by another relay that is powered by the stat which is 24 volt. That has been the problem with these old YORK units. 3 different voltages, no schematic, and it makes for a nightmare.

I was thinking that maybe the blower kicked out on thermal thus causing the overheat situation. However, it should have never got to that point of over heating unless the hi-limit is too high of specs. Will check later when the snow melts a bit more. Thanks........SS

 

[dolluper]

Re: HVAC Tech Help?

You got me thinking it's got a stat so it would have a CTI {conventional temoste interface} board with no common wire.....so no zone sensor right??
You could try 25/30/40 ton wiring simaler
www,yorkupg.com/PDFFiles/035-16682-000-0303.pdf

wiring starts on page 91 ....http:// in front of www.

 

[dolluper]

Re: HVAC Tech Help?

How did you make out??/

 

[SS MAYFLOAT]

Re: HVAC Tech Help?

I pulled the hi-limit and put it in an oven. The dang thing didn't trip until it hit 180*F. The switch is surpose to be 140*F. My supplier didn't have a manual reset for 140 so I ordered the right one from York. Our units apparently are made just for McDonalds stores, so I had to go thru the tech that is designated on those units.

I told him what I was doing. He said most stores condem the unit and get new, but there are some that do what I am doing. (Boy what a sucker I am). Instead of installing a sail switch, I'm going to install a pressure switch to switch off the stat if the fan would break a belt or a motor burn out. The sampling tube for the high pressure will be where the fan limit switch once was, and the low press sample tube will be in the fresh air return. If the fan quits, the pressure will drop and the circuit will open.

Sad part is that I've gotta wait until late next week before the limit switch comes in. I'll do an update when I get it going again I hope.

The contractor cut the bill in half. They did install a new stat and wire and that service should be paid for. The labor on the unit itself, they are going to have to eat it.

BTW, the grill that the other company said couldn't be fixed,,,,,,,,I put in a new ignition detection control and it is working as advertised. I took the one off the bad side and exchanged it with the good side. Problem moved to the other side, so that told me what part was bad. Seems like the manufactures trained tech could have figured that out. I know he had to go to the same school that I went to for these grills. It was at the factory itself. Techs are like doctors,,,,,there are good ones as well as bad ones........