S10-EV Mailing List Archive

Hello Niel I considered the defrosting of the condenser coil as well. However it does this every time you turn off the vehicle. Maybe I missed it but I have never notice the truck doing a defrosting of the coils while your using the heat pump. Its only when you turn it off or while its charging. If your not using the heat pump during charging then why would they have the defroster heat up the coils while your charging? That's what led me to the conclusion it was to remove any moisture build up in the tray. I know what you mean about a house heat pump doing this. I had a home with the heat pump condenser right outside my bedroom window. During the warm weather using the AC in the tray dry's the air there really well. Moisture or even damp air is the last thing you would want in the pack. The S-10 pack is almost a sealed unit so any humidity would have to be removed. It could be when they designed the system they thought the defrosting of the coils would work great for keeping excessive moisture out of the tray during cooler weather. It certainty works great during the warm months. When your trying to keep the pack warm its disappointing to see the AC come on in the tray. I have never timed it but I always thought it was around 5 minutes. I did find if you command the heat pump on to heat the pack the system will fault when it goes into the defrosting cycle. I agree it would have been great if they kept making the S-10. Once you get all the weak areas addressed the trucks just seem to keep running with very little maintenance. Some of you might find this interesting. As much as we fault the S-10 AC system it does have some advantages over say an open air system like the RAV4. There are many RAV drivers having problems now with due to the humidity in the air. They have great air flow but it is making current leakage worse and setting off a DTC which keeps the vehicle from charging. The S-10 actually keeps the temperatures in the tray fairly well so you don't have a catastrophic damage to the modules. It is not unusually for RAV drivers to lose at least one third of their modules. All in the same locations in the tray so its not a module problem its a design fault. Any RAV owners on this list know what I am talking about. Don In a message dated 1/28/2011 10:24:17 A.M. Pacific Standard Time, [email removed] writes: Being in Chicago, I see this all the time. I believe that the function being described is not for dehumidification, but for defrosting the front condenser coil. All home heat pumps (an air conditioner in reverse--making the outdoors colder and the indoors warmer) have to deal with frost and ice build-up on the outdoor coils. When using a heat pump at lower outdoor temperatures (typically below 45F outdoors), the temperature of the outdoor coil will often be below 32F, and frost/ice will build up in the coils, clogging the outdoor unit. When it senses a frost and ice buildup, it momentarily changes the reversing valve to A/C mode (making it hot outside and cold inside), and runs the compressor WITHOUT THE OUTDOOR FAN RUNNING to heat up the outdoor coil to melt off the frost/ice. It runs the indoor auxiliary heat during this time to prevent cold air from coming out of the furnace. Overall, it's a transfer of heat from the auxiliary heat source to the outdoor coils to melt off the frost/ice. I have a heat pump at my work, and have observed this often. The truck, which also has a heat pump to heat the cab in the winter, has a similar function. But I have to say that the truck's software is not very smart about when to activate a defrost cycle. In the truck, the "outdoor" coil is the front condenser coil. To do a defrost cycle, it sets the valving to take freon (therefore heat) from the battery box and put it in the front condenser coil, and operates the compressor for 2-3 minutes, WITHOUT the condenser fan running. The battery box is pretty much the only place it can get heat from, since it wouldn't be acceptable to take it from the cab (making the cab colder in the winter time wouldn't be tolerated). The batteries are supposedly warm and have a lot of thermal mass so they can "steal" some heat to do the defrost cycle. Again, the defrost is done without the front fan operating, just like home heat pumps. If they operated the front fan during defrost, the coils would not get anywhere near as hot, and it wouldn't melt the ice. I've never thought about that the function could be for dehumidification, but if that was the desire, they would operate the front fan to get the maximum heat transfer from the cooling coil. I'm 99% sure that the function is for defrost. On the truck's decision on when to do a defrost cycle, it seems to be triggered by sensing the key being turned off, whenever the temperature outside is low. I don't know the exact temperature that triggers it, but it's somewhere about 40-45 F. You'd think that they would do it only if you have used the heat pump during the trip, but that's not the case--it does it whenever you turn the key off and it's cold outside. It also does a defrost even if you have used only the kerosene heater. The only thing I can figure out what the designers had in mind was the possibility that you were driving in snow/ice conditions and the condenser coil in the front got coated with snow and ice (when the condenser wasn't being used), and they want to maintain it clear of ice in case you want to use the heat pump the next time you get in the truck. They figured it wouldn't be acceptable to have to wait for a 2-3 minute defrost cycle when you want heat. The heat pump uses about 1.5KW of power, so running it for 2-3 minutes is costing about 50-75 watt hours from the battery, which isn't much, considering a full pack in good condition is about 25,000 watt hours. But it's irritating to waste ANY battery power, and to make the batteries ANY colder than they already are, if it isn't necessary, especially in the winter when you're getting less energy/power from the batteries. Another down side of the current design is that the sensor for ambient air temperature is located right in front of the condenser coil. The decision on which heater to use depends on the temperature of this sensor, below 40F it uses the kerosene heater. After a defrost, and the vehicle is parked, the condenser coils from the defrost heat up the ambient air sensor, making it think that the ambient air is 60F rather than the 30F that it really is. Then when you get back in the truck and turn on the heat, it selects heat pump instead of the kerosene heater for the first 10 minutes, until the sensor cools back down to the true ambient air temperature. During this time, the output of the heater is essentially nothing, since the output of a heat pump is minuscule when it's 30F outside. So if you are running short trip errands on a cold day, you never get any heat in the cab because of this issue. Gosh, it they had only made the vehicle for a little longer and had the opportunity to work out some of these simple bugs. Sigh... But bugs and all, still way better than a dinosaur juice guzzler. Niel Hello Ryan I am use to seeing this every winter. I believe what your describing is the heat pump being used to dehumidify the battery tray. Was the temperature about 45 degrees or less? You will not see this happen in warm climates. The fan does not run while its performing this function. It will run this cycle for 5 or 10 minutes after you turn off the key. It also will dehumidify while charging under the same conditions. Your fan buffer might be fine and not having a blown fuse is a sign you don't have a problem. If it warms up a bit you can try using the AC and see if you fan comes on. Right now it is so cold keeping the pack cool is not a problem. Don In a message dated 1/26/2011 8:59:29 P.M. Pacific Standard Time, [email removed] (mailto:[email removed]) writes: All, On a very wet and humid day recently I discovered steam coming out of the front of my grill from the heat pump coil and discovered that the cooling fan wasn't spinning... I have an OEM fan buffer (I think, at least it looks OEM) and the original fan. The buffer doesn't looked burned or split open, the fuse is still in good shape. I searched the archives and read about a workaround to activate the fan when the reversing valve is active and i am curious if that has worked for others in the past or if I need to look into re-engineering or my fan buffer. I also read that Jeff had been replacing fan buffers on rebuilt vehicles and had a design to install a new and improved buffer system. Any thoughts on the subject? Ryan Dela
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