Hubesch JTD32DG dryer temp problem

[bchess]

I have recently bought six stacked JTD32DG dryers, mechanical with temp control board, and all work fine for about two weeks. Then one by one, 6 of 12 now, their max temp dropped to about 150. Have replaced cabenit limit switch, stack limit switch, and thermistor with no change. I also swapped out temp control board and an entire coin box unit, again with no improvement. Could certainly use some fresh ideas. Thanks

[MSKLAUNDRY.]

First of all that dryer is a bad choice of dryers as many on this board will tell you, but I guess you can't take it back, can you?
Since that is not and option lets see if we can help.

How do you know what the tempurature is both now and 2 weeks ago?. How are/where you measuring it?

Has you venting changed is any significant way over the past 2 weeks?
Verify what is actually shutting off, IE: temp board, thermostats, etc.

According to my books the temp sensor should read about
8990 ohms at 150 deg. and about 5000 ohms at 180 deg. I would put the one of them in the air flow stream and measure it as you use the dryer and see what the 0resistance of it is.

[bchess]

I use a low temp oven thermometer suspended from a coat hanger about 12" in from the door. When used on these machines prior to the failures I would get about 190 max with 180 normal when set on high.

[MSKLAUNDRY.]

Could that thermometer be bad, or can you notice by feeling the glass that it just ain't as hot as before?

[MSKLAUNDRY.]

Again I would verify what device is shutting off the gas and why.
Unscrew out the thermistor and run the dryer with the wires still attached and see if it gets hotter?

Just be careful!!!

[bchess]

To answer your other questions Marc the venting has been increased significantly so I don't think its a problem. As for determining where the circuit is shutting off I can't say. The one wiring diagram I had, glued on the back, blew off when we moved these units. I am trying to obtain another one now. When you say the temp sensor are you referring to the thermistor or the temp control switch. The thermistor I replaced and when I measured the control switch it had a range of 4 ohms to about 2900 ohms which was the same in one of the working units.

[MSKLAUNDRY.]

I am refering to the thermistor in the back not the control in the front.

[bchess]

I removed the thermistor and the dryer ran hotter, almost to specs. It got to 175 degrees. I contacted supplier to verify it was the right thermistor and it was. Replaced it with one out of a working unit with no change in results. When I measured them for resistance they seemed the same. Apparently it complicates the problem but I don't think its the cause. The only thing was that the specs don't even come close to what you said Marc. At about 150 degrees it registered 13k and at 175 degrees it was 10.5 K ohms. I tested more than one and all seemed alike.
????????????

P.S. I ordered a new temp control board and the wiring diagram should be here tomorrow. We'll see. Thanks for the help.

[MSKLAUNDRY.]

The thermistor resistance values I gave you were for the computer version as that is the one I have documentation for.I didn't come across those units in the field that often so I am not that sure about it. The thermistor for the rotary mech unit may be different which may account for the defference in values you measured.

[TTLES]

Do these dryers have 2 ice cube type of relays in the rear connection box ? It sounds like they are operating on "low fire". How many coils on the gas valve ?

[bchess]

The heat control relay islocated just above the temp control board on the back of coin switch assembly.

I may have located the problem. After measuring the thermistor circuit for difference in resistance value and finding none I placed a new temp control board in the machine. The thermistor is wired directly to this board so there wasn't a lot of other places to look. As near as I can tell these machines were not well maintained, they were packed with lint, and probably overheated the boards causing a resistor or diose to short. Ran the machine for an hour and it seemed to work. I'll keep you all posted. Thanks for the help