My brother's Maytag SE7800 dryer (which is stacked on a washing machine) takes about 50% longer to dry a load than it should. Extra wear on dryer & clothing and a larger electricity bill.

I haven't yet begun to diagnose it other than to clear lint from the trap and from the duct leading to the exhaust blower, and verifying that there's suction into the trap.

I saw no sign of overheating so I don't think heat is flowing along an undesirable path. This suggests one of the following possibilities:
1. The heating coil is partially broken.
2. The heating coil is being cycled off too much.
3. The hot air is being pulled out of the drum too fast.
4. The rear drum seal leaks some cooler air into the drum. (I assume a leaky front seal wouldn't be as bad as a leaky rear seal since the hot air enters the drum at the rear and exits at the front.)

I could sure use a troubleshooting guide and disassembly guide appropriate for this model. A wiring diagram and/or electrical schematic are presumably inside on one of the panels, but if someone has an image of them that would be helpful too. And I would love to have the service manual.

After I learn how to disassemble & reassemble enough of the dryer, I'll check the resistance of the heating element. Also, without disassembly, I might be able to use my multimeter's temperature probe to observe when the temperature rises & falls, to learn whether the heat is being cycled off more often than it should be.

My brother's condo is on the 7th floor of an 8-story building. A fan on the roof atop the exhaust vent runs all the time, creating additional suction. Can this negative pressure in the vent cause the heated air to be pulled out of the drum too fast? My own dryer--a Frigidaire--was designed to be used with an exhaust vent that has positive "back" pressure; the service manual says my dryer will take longer to dry using a vent with negative pressure, and says the solution would be to insert a narrow coupling between dryer & vent. So I'm wondering whether my brother's dryer might have been designed for a vent without negative pressure too. The 7th floor is near the roof fan, so if negative vent pressure is an issue with this model, I assume his dryer is likely to be affected.

My brother says the dryer has always taken a long time to dry. If that was true when the dryer was new, it would be a hint that the roof fan is the problem. But I don't know if it was true when the dryer was new because he moved into the condo 5 years ago. (Note: Where I entered the dryer's age, I was guessing when I entered "More than 10 years.")

Thanks in advance to anyone who tries to help!
Margret

Thanks, Denman, for the quick reply!

My brother washes/dries a small load every day. Intuition suggests a small load should dry much faster than a large load. But on the other hand, a small load might absorb less of the heated air, causing the exhaust to warm sooner, causing the cycling thermostat to start cycling the heat sooner. So maybe a small load won't dry much faster than a large load. So I'm wondering whether to add "small load" to the list of possible causes of "dryer takes too long."

Should drying a small load at high heat take an hour (as my brother reports) or closer to 40 minutes? When I said his dryer takes 50% longer than it should, I was assuming it should take about 40 minutes to dry his small loads.

I looked at the S1000 service manual. Much of it appears to apply to my brother's SE7800, although the SE7800 lacks the computerized controls & display and may differ in other ways I don't yet know about. I hope the reassembly instructions are the same.

Unfortunately, the troubleshooting table in the S1000 manual omits the "takes too long to dry" symptom and the SE7800 doesn't display error codes.

Regarding detaching the dryer exhaust from the wall vent for troubleshooting, it might be difficult to do for my brother's dryer; the washer/dryer is in a kitchen cubbyhole. The S1000 manual says the exhaust temperature can be measured by removing the lint trap, placing the temperature probe down into the duct, and reinserting the lint trap. Does the manual imply the dryer door should close on the probe cable? The lint trap or door might kink the cable, so I'll test first to see whether they kink cheap wire.

Thanks again,
Margret

Thanks again for another speedy reply!

I didn't mean to suggest that a small load might take longer to dry than a large load. I meant a small load might not dry as fast as one might expect. (With a large load, evaporative cooling keeps the exhaust cool, so the heat stays fully on until the load is nearly dry. A small load absorbs less of the heated air, so the exhaust heats up early, so the exhaust thermostat starts cycling the heat off and on early. This is what I observe with my dryer.)

That's a good point about the dependence of drying time on how much water was left in the clothes by the washing machine. I read a few days ago that choosing "gentle" or "delicate" on the washing machine can make drying take longer, by leaving more water in the clothes due to the reduced speed of the final spin. Another possibility is that the washing machine has a problem that causes too much water to remain in the clothes. My brother told me he chooses the "gentle" setting, and he also chooses the "medium" load size even though they're small loads, to further reduce wear on the clothes. He told me his loads don't come out of the washer overly wet, but I think I will need to judge for myself.

When you say disconnecting the dryer from the exhaust vent is the only way to rule out the vent system as a cause of drying issues, does that include ruling out negative pressure in the vent (due to the roof fan) as the cause of drying taking too long? I've gotten the impression from reading about many kinds of dryer issues that disconnecting from the vent is typically used to rule out an obstructed vent (typically lint buildup), which is the opposite of negative pressure.

If I were only trying to rule out an obstructed vent, would the following test work: Open the dryer door and, with the dryer off, place a sheet of paper over the entrance to the lint trap. If there's no significant obstruction the paper should be held firmly on the lint trap by the pull from the exhaust fan on the roof. (I already did this test, and the paper was held firmly.)

There may be a case in which disconnecting the dryer from an obstructed wall vent will fail to reveal the obstruction is causing drying to take too long, because the symptom will persist: According to a service manual for some Frigidaire models, drying can take longer if the vent system doesn't provide back pressure. With those models, disconnecting from an obstructed vent would change from too much back pressure to too little back pressure, and the symptom might not go away. (Or the difference in drying speed might be too small to clearly observe.)

Given how hard it is to disconnect my brother's dryer from the wall vent, can the troubleshooting order be rearranged to check easier causes first? Disassembling/reassembling the dryer might actually be easier than disconnecting it from the vent. It would also facilitate preventative maintenance.

If it turns out that negative pressure in the vent is a problem, would the following be a reasonable solution: Use aluminum foil to construct a cone shape, about 6 inches long and open at both ends, using enough foil to make it fairly rigid. The diameter of the cone's large opening should fit around the dryer's exhaust pipe. The diameter of the small opening should be about 2 inches... small enough to create some pressure, I hope. Duct tape the large end around the dryer's exhaust pipe, so that the cone extends backward toward the wall. Then connect the flexible duct from the wall vent to the dryer exhaust pipe with the cone inside the flexible duct.

Best wishes,
Margret