Capillary thermmostat vs. Bi-metal ones

[Tony Hwang]

Hi, While fixing our PTAC wall mount Carrier unit in sun room, I wondered I can replace SPDT capillary thermostat for heat/cool running on 220V AC. Unit contains

6KW rated heating element/heat pump. Is it possible to replace original capillary thermostat with line voltage SPDT thermostat? Tired of replacing original capillary thermostat at 70.00 a pop. Heating switch contact keeps burning up, p/n HH22UC075. Or I wonder if there is heavier Carrier substitute part no.?

[trader_4]

Not sure what the question really is. If the replacement thermostat has at least the rating of the original, it will work electrically. The rest is if it's a different type, where does it sense the air? If the old one has a capillary probe that sits in the air and the new one doesn't then it may behave differently. There is also the issue of will it fit physically. And finally, I guess the issue of modifying a UL listed AC, if you want to get technical. I wonder if the reason they burn out is that the compressor is starting to go and is harder to start? Maybe time for a hard start kit.

[Tony Hwang]

Hi, When weather gets cold heat pump does not come on,but heater is on. Compressor (cool) side contact is always good. Maybe I should put in spark suppressor across heat contact then... Was just thinking. Capillary probe is sensing intake room air temp near the filter. . I was thinking about extending 3 wires for the thermostat to wall mounted line voltage type NO/NC SPDT type 'stat/ Actually another model of this unit has this remote 'stat option kit. Maybe that is what I need, come to think of it. Just exercising my brain for now.

[hrhofmann]

Please enlighten me, what is a capillary thermostat? Do you mean a mercury bottle thermostat?

[Stormin Mormon]

What volts and amps do you need? And it the stat for heating?

[Ed Pawlowski]

Bi metal is two unlike metal sandwiched together and they expand at different rates causing it to bend. That is the types use is the round Honeywell T-stats in many homes.

mercury expands in a tube or bulb. It can register degrees in a long tube as an indicator.

Capillary is a thin piece of tubing with usually a bulb of some sort at one end. As the material inside expand, it pushes a diaphragm and can operate a tiny switch to make or break a contact. Refrigerators use that type. Others for gas appliances have a bellows that can work a valve to control the gas. No electricity needed.

The liquid inside is some sort of silicone than can take both high and low temperatures.

[Tony Hwang]

Hi, This is Carrier PTAC wall mount they quit producing in 2009. Heat pump and 6KW heat strip combo for heat/cool. Works well for our sun room separate from house HVAC also Carrier. Replacing thermostat is PITA, has to take cover off, control panel off,etc.

3 connectors. I was thing about extending those 3 wires to a higher wall position and use line voltage 'stat which is easier to get. Also I'm thinking about snubber across heat contact to protect the contatcts from burning(which is the issue) Snubber is easy to jury rig. A resister and capacitor in series.

[hrhofmann]

Ed - Thanx - I've seen the capillary types, never thought about how they worked. Everything I have ever had to work on was the standard bimetallic type.

[Tony Hwang]

Hi, Follow up, I put in OEM replacement parts this time in ahurry but I installed snubber across heat contacts and will see it helps. Fixed the unit in a hurry and well, looks like we are in Indian summer now...