My Wife's car seems to have an issue on long trips with the A/C. Generally around town it is fine and blows cold. However, on some long freeway trips, the ac air will become warmer and the flow from the vents will slow. When I switch the a/c off, the air gets colder for a bit and the normal air flow resumes and then warms up. Once I turn the a/c back on, the air gets cold again for about an hour or so and then the situation repeats itelf. So during a 250 mile trip, I had to cycle the a/c about 4 or 5 times... Any ideas on what could be causing this? My first thought was that it was getting too cold and freezing up the lines, similar to a window a/c. On another trip, I checked the lines and there was a lot of condensation on them, (Trip to the AZ desert) and a lot of water was draining from the system.
Question about A/C ...
- Thread starter MysticGold04
- Start date
- Status
Your evaporator is icing up. My old Jag does this pretty often and has the same symptoms. The hot outside air passes over a radiator-like device in the air box under the dash. When run continuously in a relatively humid climate, the evaporator gets so cold that the condensation freezes up in the little fins and eventually becomes a big block of ice, blocking the air flow.
When its warm and raining in Seattle (doesn't happen all that often), I have to cycle the system on and off on long drives.
Also, make sure the drain tubes for the A/C box are not plugged.
Hope this helps!
When its warm and raining in Seattle (doesn't happen all that often), I have to cycle the system on and off on long drives.
Also, make sure the drain tubes for the A/C box are not plugged.
Hope this helps!
There is supposed to be a pressure switch which cuts off the power to the AC clutch to prevent freezing of the evaporator coil.
Tried that, it still does it in either recirc or fresh mode.
I do not think any of the drain pipes are blocked, because I can see water coming out... Just seems strange that it just started all of a sudden this summer.. Only thing I've changed is the micron filter at the beginning of summer and I know I installed that right... only goes in one way.
I'm not positive but I think that switch is only if there is condensation in the actual A/C line that has frozen.. The system would never know if the outside of the evaporator has frozen from the condensation it is extracting.
If its still under warranty the manufacturer may have a fix for this problem. If this car has the problem, I'm sure lots of others do too. They'll probably replace the expansion valve or orifice tube with one that will either make the system cycle more slowly or not allow as much refridgerant through into the evaporator making it not as cold.
easier fix is to vent a bit of refrigerant untill the problem goes away.
[quoteI'm not positive but I think that switch is only if there is condensation in the actual A/C line that has frozen.. The system would never know if the outside of the evaporator has frozen from the condensation it is extracting.
It's a low-pressure cutoff switch. The pressure is directly related to the temperature of the evaporator coil. If the pressure drops too low it is supposed to cut power to the AC compressor clutch, disengaging it until the pressure rises again (as the evaporator warms up). This switch additionaly serves the purpose of keeping the compressor from engaging if the refrigerant charge is low.
A similar device is used on commercial/residential air conditioners to allow them to be used during cold weather. You might want to do that if you were trying to keep a data center cool in winter. Without that device, which by the way is optional, the evaporator coil WILL freeze up in winter. Had that happen at my last job. They installed a low pressure switch wired to cut power to the outdoor unit's fan, so if the evaporator coil's temp got too low the switch would cut the outdoor unit's fan off until it's temp increased again.
One day during summer I had to hose those outdoor units off while they were still operating because the coils were just about clogged with pollen. Interestingly, as I sprayed water on the condensor coil, the fan turned off and you could see the water evaporating from the coils as the compressor's sound changed tone (as though it were working harder) and a few seconds later the fan turned back on. Apparently the action of spraying water on the outdoor coils lowered the pressure enough that the low-pressure switch cut off the fan.
It's a low-pressure cutoff switch. The pressure is directly related to the temperature of the evaporator coil. If the pressure drops too low it is supposed to cut power to the AC compressor clutch, disengaging it until the pressure rises again (as the evaporator warms up). This switch additionaly serves the purpose of keeping the compressor from engaging if the refrigerant charge is low.
A similar device is used on commercial/residential air conditioners to allow them to be used during cold weather. You might want to do that if you were trying to keep a data center cool in winter. Without that device, which by the way is optional, the evaporator coil WILL freeze up in winter. Had that happen at my last job. They installed a low pressure switch wired to cut power to the outdoor unit's fan, so if the evaporator coil's temp got too low the switch would cut the outdoor unit's fan off until it's temp increased again.
One day during summer I had to hose those outdoor units off while they were still operating because the coils were just about clogged with pollen. Interestingly, as I sprayed water on the condensor coil, the fan turned off and you could see the water evaporating from the coils as the compressor's sound changed tone (as though it were working harder) and a few seconds later the fan turned back on. Apparently the action of spraying water on the outdoor coils lowered the pressure enough that the low-pressure switch cut off the fan.
Iiiiinteresting. Thanks for the info. I've seen the low-pressure switches on every auto A/C I've ever worked on, but never knew it could double as a sensor for the evaporator. I'll watch for that!
Come to think of it though, the Jag's low-pressure switch works fine (as the pressure gets low every couple years) but it doesn't stop the compressor when it ices up. Must not be set up the same way.
Come to think of it though, the Jag's low-pressure switch works fine (as the pressure gets low every couple years) but it doesn't stop the compressor when it ices up. Must not be set up the same way.
The low pressure switch is not cycling correctly. Some are adjustable and others you just replace. 99% of them can be replaced w/o losing and refrigerant.
Yep.. going in to the dealer today, its still under warranty.. and also because the belt tensioner is making alot of noise. They just replaced the tensioner 2 weeks ago.. and back it goes...
That's interesting . . . Thanks
- Status
Similar threads
