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View Full Version : Hotpoint Fridge Freezer (thermistor problem) -- Mistral FF91



Xad
06-09-2012, 12:41 AM
I have a Hotpoint Mistral FF91S Fridge Freezer. Many years ago i ran into the problem where the fridge would not get cold, but the freezer would. Replacing both green and yellow thermistors fixed that problem.

Fast forward 5 years, i experienced the same problem, problem is, can't find the green thermistor anywhere, out of stock, so i purchased the yellow thermistor seeing as the freezer seemed to be working fine thought it would be worth a try.

Installed the Yellow thermistor and it worked....for about 3 days, now the Fridge is back to NOT cooling again and weirdly, the freezer instead of going down to -22c it goes to about -14c and no lower. Fridge is room temperature. I tried disconnecting the Thermistors and reattaching them. No excessive ice build up or anything.

1. Did i kill the new Yellow thermistor because i didn't change the green one as well? Is that even possible?
2. Why did it work perfectly for 3 days only to stop?
3. Or will replacing the Green thermistor fix this?

tonto33
06-09-2012, 01:50 PM
u need to replace both at the same time

Xad
06-09-2012, 03:27 PM
u need to replace both at the same timeAlready ordered the green one this morning, should be here tomorrow. Paid double the price i paid previously, guessing because of the shortage.

Any idea as to whether the new yellow thermistor will have been affected in a negative way since the green one wasn't replaced when i installed the yellow one? As in become faulty even though it's new? The fridge and freezer were working perfectly for about 3 days until it became faulty again (fridge not cooling).

Xad
08-09-2012, 11:46 AM
Yesterday morning i replaced the Green Thermistor with a new one (replaced the Yellow earlier as mentioned); however, it has made no difference as the fridge is still at room temperature and the freezer is still not at -22 instead hovers around -14.

I did notice a small crack along where one of the food storage compartments slides in, no one can tell me whether that was there before the fault or only just appeared, however, yesterday i covered it up with some aluminium tape but it has made no difference.

Any ideas?

Xad
10-09-2012, 08:09 PM
Put a bowl of boiling water on top of a towel inside the freezer for about 3 hours, then took it out and left the doors open overnight; then turned the unit on in the afternoon with nothing in, and unfortunately it still didn't work. Freezers still hovering around -14c instead of -22c for some reason and keeps getting slight warmer only to return to -14c. Fridge is room temperature and has no cool air circulating.

So both Yellow and Green Thermistors replaced.
Small crack sealed with layers of aluminium tape.
Manually defrosted.

And still not working. Anyone have any ideas? Went instore to buy a new one today, wouldn't mind trying one more time to fix the faulty one before it goes to it's final grave.

Someone was telling me apparently freezers can lose some kind of gas in which case they might need refilling? Is that the case for frost free fridge freezers? Again, it's a Hotpoint FF91S.

tonto33
11-09-2012, 08:17 AM
may need regas

Xad
22-09-2012, 03:55 AM
So i bought a new fridge freezer, Hotpoint FUFL2010p and it makes a lot of cracking/popping noises constantly so thinking about returning it. Is that the norm? Read somewhere it's to do with the R600a gas that's used nowadays? But then, not all FF make this annoying sound...

Still have the old Mistral. Being that it needs a regas, which is most likely the case, does that mean there's a leak along the piping somewhere? Do freezer repair people usually fix leaks too? I think the leak might be on the inside as opposed to the back...as in, the freezer compartment where the thermistors are, the left side though where the copper piping comes in.

Although, if there is a leak, shouldn't all of the gas have escaped? Hence the freezer should be at room temperature also? I'm guessing the past few weeks haven't helped the compressor as it sounds like it's been going 100% non stop. Also, strangely, the freezer has reached -22c once or twice with the fridge also cooling, but then returned to square one.

On a sidenote, the back of the fridge freezer is covered up; how do you even take it off? Do you just pull it off? It's in two parts, the large metal backing covering 85% of the back and looks fixed, and then about 15% of it, the bottom where the compressor is, is plastic -- seems flimsy. Is it just pulled off?

Mad_angler1
22-09-2012, 09:44 AM
So i bought a new fridge freezer, Hotpoint FUFL2010p and it makes a lot of cracking/popping noises constantly so thinking about returning it. Is that the norm? Read somewhere it's to do with the R600a gas that's used nowadays? But then, not all FF make this annoying sound...

Still have the old Mistral. Being that it needs a regas, which is most likely the case, does that mean there's a leak along the piping somewhere? Do freezer repair people usually fix leaks too? I think the leak might be on the inside as opposed to the back...as in, the freezer compartment where the thermistors are, the left side though where the copper piping comes in.

Although, if there is a leak, shouldn't all of the gas have escaped? Hence the freezer should be at room temperature also? I'm guessing the past few weeks haven't helped the compressor as it sounds like it's been going 100% non stop. Also, strangely, the freezer has reached -22c once or twice with the fridge also cooling, but then returned to square one.

On a sidenote, the back of the fridge freezer is covered up; how do you even take it off? Do you just pull it off? It's in two parts, the large metal backing covering 85% of the back and looks fixed, and then about 15% of it, the bottom where the compressor is, is plastic -- seems flimsy. Is it just pulled off?

The cracking sounds are normal. Due to the rapid expansion and contraction during defrost.

As for the older unit I believe this is the model with the coiled condenser in the base. Is the fan running to cool this ?. If this fails it won't be able to fully cool due to over heating and won't fully chill. Make sure the air ducts in front at the bottom are also clear.

Xad
22-09-2012, 01:53 PM
Does the cracking noise exist in all new fridge freezers? Is it to do with the R600a refrigerant? The old mistral didn't make this much noise for this long, but that used R134a; is that supposed make less noise?

Not sure if the fan next to the compressor is running, not even sure how to get to it as it's covered with a black plastic with no screws in sight. I'm guessing it's just pulled off? Will have a look. BTW i made a mistake, it's an FF92S, not a FF91, think they're similar anyway.

I think i may have caused the leak when i turned it off and held a hair dryer inside the freezer; there's a copper connection (photo below) soldered on the left side right in front of the duct that goes to the fridge i think (small copper pipe goes into a large one) and i think because i held the hair dryer there while the pipe was still frozen (but mains turned off), the large pipe may have expanded too quickly hence causing the solder joint to break and let some gas out.

That's a complete guess, but would make sense as initially the freezer was working fine and it was just a standard thermistor replacement fault, but when i turned the FF off and used a hair dryer and then turned it back on, the temperature stopped getting to -22c instead it just stayed at -14c and now it just fluctuates all over the place but mainly stays around -14c.


https://dl.dropbox.com/u/1123710/FF92S-1.jpg


And here's the same joint 6 years ago, i took a photo of the back of the freezer when i was replacing the thermistors:
https://dl.dropbox.com/u/1123710/FF92S-2.jpg
Not sure what the black material is, could be another joint issue in there even.

Mad_angler1
22-09-2012, 07:12 PM
The cracking is nothing to do with r600 it's self but the liners are made of a different foam. But it's just down t the design now rather than the gas it's self

TBH you would need to see that joint and vac test it. From the sound of it it's a gas issue. As it 134 I would not bother.

As for the fan running look through the front grill and you can see tight through to the back. You should be able to see it running.

Xad
22-09-2012, 07:25 PM
Might be why the new Hotpoint was cheaper than other Hotpoints available with pretty much the exact same specs, cheaper foam and possible noise complaints.

How come you say you wouldn't bother with 134 gas? Is it because it's not as good? More dangerous?

I think you're right and a new FF was the right course of action, unfortunately ended up buying one that loves to make cracking noises. The humming noise is fine, but the cracking noise is really annoying. I'm guessing the cracking noise is permanent and it won't disappear over time?

tonto33
23-09-2012, 05:17 PM
where bouts are you mite know a engineer near u who could take look at tell you excate fault

Mad_angler1
23-09-2012, 10:30 PM
Might be why the new Hotpoint was cheaper than other Hotpoints available with pretty much the exact same specs, cheaper foam and possible noise complaints.

How come you say you wouldn't bother with 134 gas? Is it because it's not as good? More dangerous?

I think you're right and a new FF was the right course of action, unfortunately ended up buying one that loves to make cracking noises. The humming noise is fine, but the cracking noise is really annoying. I'm guessing the cracking noise is permanent and it won't disappear over time?

The cracking can settle over time, the foam is changes due to the change in gas from hfc to r600a isobutane,

as for 134a i no longer work with it, i only do R600 since the F-gas regs came in

install monkey
23-09-2012, 10:35 PM
you need to prove the condenser fan is running- as its 5yr old and you were unsure it was working

Xad
24-09-2012, 02:47 AM
I finally had a check of the front grill with a torch light, couldn't see through as there was a surprising amount of dust build up...a wall of dust.

Opened up the front grill and got an even bigger shock as there were multiple handfuls of dust built up...11 years worth :eek: Took most of it out.

Opened up the back plastic (two screws on the bottom) and the fan is spinning. It's close to the compressor but facing forward in the direction of the front grill, i'm guessing it pulls the hot air out away from the compressor rather than cooling the compressor by facing it.

Going to see if it makes a difference in the morning. I'm guessing the compressor/freezer must have been working very inefficiently all these years as it's not been cooling as it's supposed to for a few years :eek:

Xad
25-09-2012, 01:12 AM
Unfortunately it didn't make a difference; fridge still not working and freezer hovered around -19c max and it's started to make a rumbling/vibration noise from the fan now (or compressor?), as in: normal motor sound for 3 seconds, rumbling motor noise 3 seconds, normal, rumbling etc. Maybe the fan needs a good clean or repositioning, possible vibration issue.

Either way, switched it off, going to get rid of it now and keep the new one as i'm guessing Currys will charge quite a bit to have it returned even under the 7 day distance selling rule. Shame about the cracking noise, hopefully it settles down over time.