Lennox HS-21 Help

[SandShark]

My ex-boss just called me on an issue he's having with a long-time customer's HS-21 that I used to do all the service calls on because he was my Pony League baseball coach way back in the day. Anyway, the issue, as he described it, is that he think he's diagnosed a defective temperature sensor (S1 and S2) on this HS21-048 and was asking if I knew how to bypass the sensor temporarily to see if he could verify it is the sensor or not. I was thinking S1 and S2 could be jumped on the 2-speed controller using a resistor, but I wasn't exactly sure which ohm resistor to use and even if that would do the trick or not. Anyone ever had success jumping out the sensor on one of these 2-speed controls? If so, how did you do it? Thanks!

[dandyme]

On all units using the TSC two-speed control, terminals
S1 and S2 on the control are connected to temperature
sensors (thermistors) which monitor the temperature of
the compressor motor windings. The two-speed control
measures the resistance through the sensors. The sensors
increase their resistance as temperature increases
(for example, too much superheat). When the resistance
through the sensors increases above a preset limit, the
control stops compressor operation for a minimum of
five minutes. As the compressor windings cool, the resistance
through the sensors drops below the reset
limit, the control resets automatically and one fault is
counted.
Page 10
Check sensors by measuring resistance (ohms) through
the sensors with the wires disconnected from the control
(unit not running). The sensor wires are not polarity sensitive.
Table 3 shows winding temperature sensor
resistance values which will cause the TSC to lock out.
When unit is operating normally, resistance through the
sensors should be below the trip value shown in table 3.
TABLE 3
Compressor Winding
Temperature Sensor TSC−5 Copeland Compressor

Trip Ohms
Temp
Rise 25K − 35K


Reset Ohms
Temp Fall 8.4K − 10K


Normal
Ohms 90 − 7800

[mark beiser]

A 5kohm resistor across S1 and S2 will get them going until the compressor/system can be replaced.
Be aware that bypassing the sensor leaves the compressor/wiring with no overload protection.

I've found failed sensors a handful of times, usually open, but I had one that was reading >70k in a very cold compressor.

Carrier/Bryant also used that Copeland 2 speed compressor in some units in the late 90's.
Goodman used the Bristol 2 speed for a while, its sensor works pretty much the same way.

[SandShark]

A 5kohm resistor across S1 and S2 will get them going until the compressor/system can be replaced.
Be aware that bypassing the sensor leaves the compressor/wiring with no overload protection.

I've found failed sensors a handful of times, usually open, but I had one that was reading >70k in a very cold compressor.

Carrier/Bryant also used that Copeland 2 speed compressor in some units in the late 90's.
Goodman used the Bristol 2 speed for a while, its sensor works pretty much the same way.Hey, much appreciated. It'll be up to him as to whether or not to leave it jumped out. I'll call and give him the info.

Thanks again!

[mark beiser]

2 speed tip:
If you come up on one that is locked out from over heating, you don't have to wait for it cool enough to reset before you can troubleshoot it.
Just bypass the sensor with a 5k ohm resistor long enough to troubleshoot it.
If it was something obvious like a blown run cap and start kit, repair it, then fire it up with the sensor bypassed for long enough for the suction gas to cool the compressor windings enough to get the resistance through the sensor down below 8k ohms or so.

The later HS/HP14, and HS/HP21 units will lock out after a few trips, so typically won't be hot when you get to them, but the older HS/HP14 units, and previous generations, that have the Texas Instruments protection module, don't go into a hard lockout.

[SandShark]

Excellent! Thanks again.

[jimj]

Your showing your age talking about HP14's. LOL

[mark beiser]

Your showing your age talking about HP14's. LOL

I started out working for Lennox dealers that sold a TON of 2 speed equipment and Pulse furnaces in their day.
I worked on so many of both that I thought they were rather common.
Then I stopped working for Lennox dealers and found out how wrong I was. :)

My favorite were the first and 2nd generation HP11, with the electromechanical demand defrost system that would make Rub Goldberg proud.

The first generation HP14, the one with air intake on 2 sides and discharge on 2 sides with the outdoor fan diagonal through the middle, was just as cool, but was annoying to work on because you had to take both louvered intake panels off to check the refrigerant.
The HP14 became less interesting when they "simplified" the defrost system by moving most of the switching from contacts on electromechanical timers to a couple of triple pole double throw relays, and downright boring when the last generation of them switched to the "grey box" control module and electronic demand defrost.
I was always baffled as to why they didn't change the model from HS/HP14 to something else when they switched from the dual side intake/discharge to top discharge.

One of my very first service calls as a newly minted service tech was a no cooling call for a HP14 + Pulse G14 dual fuel system with the old Lennox OK Fuelmaster dual fuel control and first generation Lennox Flexstat.
I opened the panel and...:Faint:

[SandShark]

I started out working for Lennox dealers that sold a TON of 2 speed equipment and Pulse furnaces in their day.
I worked on so many of both that I thought they were rather common.
Then I stopped working for Lennox dealers and found out how wrong I was. :)

My favorite were the first and 2nd generation HP11, with the electromechanical demand defrost system that would make Rub Goldberg proud.

The first generation HP14, the one with air intake on 2 sides and discharge on 2 sides with the outdoor fan diagonal through the middle, was just as cool, but was annoying to work on because you had to take both louvered intake panels off to check the refrigerant.
The HP14 became less interesting when they "simplified" the defrost system by moving most of the switching from contacts on electromechanical timers to a couple of triple pole double throw relays, and downright boring when the last generation of them switched to the "grey box" control module and electronic demand defrost.
I was always baffled as to why they didn't change the model from HS/HP14 to something else when they switched from the dual side intake/discharge to top discharge.

One of my very first service calls as a newly minted service tech was a no cooling call for a HP14 + Pulse G14 dual fuel system with the old Lennox OK Fuelmaster dual fuel control and first generation Lennox Flexstat.
I opened the panel and...:Faint:Yeah, I worked on a few HP14s in my day and maybe a few HP11s, too. Here's a thread with some HP14 photos for your viewing pleasure. Ewww... :eek2:

http://hvac-talk.com/vbb/showthread.php?t=285582

[mark beiser]

Yeah, I worked on a few HP14s in my day and maybe a few HP11s, too. Here's a thread with some HP14 photos for your viewing pleasure. Ewww... :eek2:

http://hvac-talk.com/vbb/showthread.php?t=285582

I've got a customer that has an HS14 and a Pulse G14, it is a later top discharge HS14, but is pre "grey box" control module.
Both still have all of their original parts, except for fan motors and normal wear items on the Pulse. By some strange fluke rift in the space time continuum, The unit still has its original start winding current limiting thermistor...

It has been a looooong time since I've seen an HS/HP11 or a side discharge HS/HP14 though. :(

[SandShark]

I thought I would update the thread in case anyone is interested.

I learned today that placing a 4.8K ohm resistor across the controller S1 and S2 terminals didn't solve the issue. Ex-boss is p'oed, not so much for the fact that he didn't get the unit running using the resistor, but the fact that Lennox tech support suggestions to fix the issue were no help. Not only that, he's leaving the area for a week, so he had to reluctantly tell a long-time customer to call another company. Oh, well...

[mark beiser]

Well, the resistor trick only works if you have a bad sensor AND the two speed control is sending the appropriate voltage to it.
If the sensor is good, but the two speed control is bad, it obviously does no good to jumper out the sensor.

Did he ohm out the sensor, or check that the control sends voltage to it?

[jimj]

If you get a chance to go back maybe this will help. The flow chart on page 16 can really help!

[Senior1]

I opened the panel and...:Faint:

LOL,,that made me laugh, I remember a GE RTU, about 50 ton HP in the 80's or so, opened the panel and all black wires with 30 relays:gah:

[mark beiser]

LOL,,that made me laugh, I remember a GE RTU, about 50 ton HP in the 80's or so, opened the panel and all black wires with 30 relays:gah:

Mix in one of those old Honeywell energy management system logic panels and it's a real party!

[SandShark]

Well, the resistor trick only works if you have a bad sensor AND the two speed control is sending the appropriate voltage to it.
If the sensor is good, but the two speed control is bad, it obviously does no good to jumper out the sensor.

Did he ohm out the sensor, or check that the control sends voltage to it?It is my understanding he did ohm out the sensor and the sensor ohm value was below the trip value listed in Table 4 in the service literature. Supposedly, he found a new two-speed controller at the shop and installed it with no joy. He told me he didn't know why he had a new two-speed controller because that's not something he would normally have on hand, but at the time I didn't put two and two together. After I thought about it, I'm betting the controller at the shop was one that I had changed out for warranty and put on the shelf waiting to ship it back to Lennox. Lennox, however, doesn't require all warranty parts to be shipped back, but they do ask that the parts are kept for a certain amount of time, just in case they do want them back. But, by the time I thought about it, it was too late. He's out of the country now.

[mark beiser]

:LOL:

Been there, done that!:gah:

Because of similar confusion over new looking, but bad parts, I started marking all side of any box that contains a defective part, and writing "D" on the part number label.

I do this every time I change any part, even if it is going in the trash bin.
The old part immediately goes into the box the new one came out of, and out comes the Sharpie to mark the box.