Cab Heat / Air Conditioning Issue

[NetbyTractor]

I noticed something odd relative to this topic this morning. Today was one of the coldest mornings that I have used my tractor - about 10 F. When I first got in, I turned on defrost and tried to toggle the AC button. No light. After running it for a little while, I tried it again, and the light toggled. My theory is that the AC is not allowed to be turned on below a certain temperature in order to protect the AC system. After the tractor ran a bit, it warmed up everything enough to be above the disable threshold.

 

[Threepoint]

I noticed something odd relative to this topic this morning. Today was one of the coldest mornings that I have used my tractor - about 10 F. When I first got in, I turned on defrost and tried to toggle the AC button. No light. After running it for a little while, I tried it again, and the light toggled. My theory is that the AC is not allowed to be turned on below a certain temperature in order to protect the AC system. After the tractor ran a bit, it warmed up everything enough to be above the disable threshold.

Interesting idea, although that sounds like a rather sophisticated feature for a CUT HVAC system. Hopefully others will weigh in on this and we'll at least get some more data points to test it. Maybe Kioti617 will jump in to let us know whether ambient temperature might be a factor in his case also. Don't know his location from his profile. Here in Northern Virginia, and with my tractors kept in garage and barn bays, I thankfully don't have the opportunity to do an empirical investigation of this. :laughing:

 

[Kioti Dave]

Interesting idea, although that sounds like a rather sophisticated feature for a CUT HVAC system. Hopefully others will weigh in on this and we'll at least get some more data points to test it. Maybe Kioti617 will jump in to let us know whether ambient temperature might be a factor in his case also. Don't know his location from his profile. Here in Northern Virginia, and with my tractors kept in garage and barn bays, I thankfully don't have the opportunity to do an empirical investigation of this. :laughing:

My NX seems to act this way as well. If really cold, will not turn on. After you get some heat going, will work.

 

[MinnesotaEric]

I noticed something odd relative to this topic this morning. Today was one of the coldest mornings that I have used my tractor - about 10 F. When I first got in, I turned on defrost and tried to toggle the AC button. No light. After running it for a little while, I tried it again, and the light toggled. My theory is that the AC is not allowed to be turned on below a certain temperature in order to protect the AC system. After the tractor ran a bit, it warmed up everything enough to be above the disable threshold.

That is correct. The thermister, that works as a temperature switch for the AC in our tractors, must be warm enough before allowing to AC pump to turn on and begin drying the air for defrost. If the thermistor did not do this, the AC refrigerant would slug the compressor. Yesterday while blowing and plowing my tractor didn't kick its AC on until maybe 15-20 minutes of work and this with a block heater on for over 24 hours.

 

[Threepoint]

That is correct. The thermister, that works as a temperature switch for the AC in our tractors, must be warm enough before allowing to AC pump to turn on and begin drying the air for defrost. If the thermistor did not do this, the AC refrigerant would slug the compressor. Yesterday while blowing and plowing my tractor didn't kick its AC on until maybe 15-20 minutes of work and this with a block heater on for over 24 hours.

Sounds like the HVAC system is well thought out in this regard. I'd be curious to know what the thermistor set point is. :scratchchin: Morning air temp around here occasionally is in the high teens or low twenties. Sometime much lower. But balmy by comparison to what many TBNr's regularly experience. :cold:

Eric and Kioti Dave, during your minutes of work before the AC switches on, have you experienced much fogging on the glass?

 

[MinnesotaEric]

Sounds like the HVAC system is well thought out in this regard. I'd be curious to know what the thermistor set point is. :scratchchin: Morning air temp around here occasionally is in the high teens or low twenties. Sometime much lower. But balmy by comparison to what many TBNr's regularly experience. :cold:

Eric and Kioti Dave, during your minutes of work before the AC switches on, have you experienced much fogging on the glass?

Sadly, it fogs all over the place until the underhood or cap top temperature rises high enough to cut in the AC compressor to start drying the air (I have no idea where the thermistor is located in our application). Thermisters are the cheap version and somewhat more reliable version of a traditional mercury temperature switch. AC systems have at least one temp or limiting switches: a cut in and sometimes a second cut out switch to protect an overheating system. Cut in is the cold side, cut out is the hot side. Cars nowadays may have humidity switches and solar load sensors in addition to fine-tune the driver's comfort.

 

[Kioti Dave]

Sounds like the HVAC system is well thought out in this regard. I'd be curious to know what the thermistor set point is. :scratchchin: Morning air temp around here occasionally is in the high teens or low twenties. Sometime much lower. But balmy by comparison to what many TBNr's regularly experience. :cold:

Eric and Kioti Dave, during your minutes of work before the AC switches on, have you experienced much fogging on the glass?

Unfortunately, yes I do get some fogging. I have a 12 volt fan that I use to keep the rear window clear. That helps. Once the A/C starts to work, clears up really quick. I did have to get the warranty work done on the blend gates on top of cab to be able to blow warm air while A/C on.

 

[Threepoint]

Sadly, it fogs all over the place until the underhood or cap top temperature rises high enough to cut in the AC compressor to start drying the air (I have no idea where the thermistor is located in our application). Thermisters are the cheap version and somewhat more reliable version of a traditional mercury temperature switch. AC systems have at least one temp or limiting switches: a cut in and sometimes a second cut out switch to protect an overheating system. Cut in is the cold side, cut out is the hot side. Cars nowadays may have humidity switches and solar load sensors in addition to fine-tune the driver's comfort.

Perhaps this. Attached is a description of the "Thermocon" operation in the NX HVAC system. If I'm interpreting it correctly, the thermistor's set point is nominally 32 F. So, if it senses an ambient temp in the roof cap below that, the AC relay will not switch on. Does that sound right?



Since some are reporting no illumination of the AC indicator light prior to warm up, the light evidently is wired between the thermistor and the AC relay, thus will not illuminate below 32 F. That seems a bit odd, though, as more logically I would expect it to illuminate whenever there is power to the thermistor. Then, as the roof cap temp reaches the set point, the thermistor would allow current to flow to the AC relay, while the light stays lit the entire time until the AC switch is toggled off.

But, then, I'm no electrical design engineer, so I may be all wet on all of this. :laughing:

 

[Kioti Dave]

Perhaps this. Attached is a description of the "Thermocon" operation in the NX HVAC system. If I'm interpreting it correctly, the thermistor's set point is nominally 32 F. So, if it senses an ambient temp in the roof cap below that, the AC relay will not switch on. Does that sound right?

View attachment 637948

Since some are reporting no illumination of the AC indicator light prior to warm up, the light evidently is wired between the thermistor and the AC relay, thus will not illuminate below 32 F. That seems a bit odd, though, as more logically I would expect it to illuminate whenever there is power to the thermistor. Then, as the roof cap temp reaches the set point, the thermistor would allow current to flow to the AC relay, while the light stays lit the entire time until the AC switch is toggled off.

But, then, I'm no electrical design engineer, so I may be all wet on all of this. :laughing:

My A/C indicator light will not go on if A/C is not operating.

 

[Kioti Dave]

A question related to this topic. Is there a max temp that will cause the A/C to cut out??