A/C not working in cold temps.

[kiotiken]

I use my A/C with heat to keep the cab fog free. Earlier this winter and now consistently during our latest little cold snap, the A/C will not come on. The first time it happened, I checked the fuse and it was fine and then after using the tractor for about 20 minutes (after it had warmed up for an initial 20 minutes), it all of a sudden came on. It's been the same story every subsequent time, push the button, nothing happens (the little light on the button doesn't even light up) but after some period of time, it kicks in. My dealer said he didn't know if that was normal and it had to warm up first but he would look at it. To me, that doesn't sound right at all and I don't remember anything similar from last winter. Does anybody know if there's some sensor that prevents the A/C from working for some period of time or until the engine has warmed to some temp? I always allow the engine temp to come up to normal range with the PTO engaged to help warm the oil before using the tractor.

 

[Midniteoyl]

A/C in car/trucks wont come on below a certain temp to avoid icing.. I know in my Audi, it was 0c degrees and some cars are 4c.. The temp sensor on yours must be under the hood so when the engine bay heats up, it comes on.

 

[unimog_jason]

The sensor has to read above 5C before the AC will kick in. On my DK40 I turn the switch AC on, crank the heat on high and let the tractor warm up and by the time I get back to the tractor the AC is working.

Jason

 

[kiotiken]

OK, thanks guys. Maybe it's just been really cold lately, but it's taken upwards of 40 minutes run time to come up to that temp including warm up.

 

[cbailey1956]

Sounds normal to me. Most cab units have an overhead evaporator and heating coil combined. Their is a temp sensor that keeps the evaporator from freezing up when the A/C is on. It turns off the compressor, prevents the evaporator from turning into a block of ice and not allowing air flow over the coils. In winter its sensing the cold untill the heater core warms it up enough to power the compressor. Are you running a block heater to keep the coolant warm? Fan on high will help speed the process.

 

[grm61]

The light should still come on??
Mine does anyway, even when it is to cold for the compressor to cycle.
I need to warm my tractor up before I turn the temp knob up for the heater.
If I start the tractor when it is bitter cold, turn on the heat and walk away for 20 min it will barely be off cold.
If I leave the heat off, the coolant temp will come up to the middle in15 min or so,then if bring the revs up to 1500 or so turn then temp up and the guage will say between the dots.
If I drop it to idle with the fan cranked up, it will pull the gauge all the way back to cold after a few minutes at low idle.
So I try and get the coolant temp up first before turning the heat on, then run it to keep it up between the dots.

This is how it was the day I ran it at 0 F.

 

[unimog_jason]

The light on my AC switch doesn't light up until the sensor is warm and it takes a while for everything to get warm enough to make the AC kick in.

We've been having some rather cold weather recently and I find my tractor acting the same as yours. If I'm blowing snow, the temp gauge will be between the dots and I get lots of heat, but as soon as I unload the engine, it quickly cools off.

Jason

 

[cbailey1956]

My opinion that most tractors have oversized cooling systems, unlike cars that must warm up quickly for emissions to drop. I rarely see them run hot under normal conditions. As long as coolant levels within range and radiators not completely clogged. That said it just takes a long time to warm up as they are so efficient at getting rid of engine heat. You might try the old trick of cardboard or plywood in front of the radiator to block airflow until the engine coolant is up to temp. When the A/C comp is engaged you are actually cooling the evaporator the same time as hot water is trying to heat the evaporator. The refrigerant is still flowing through the evaporator and cooling the hot water until it gets warm enough to overcome the refrigerant ability to cool. So with A/C engaged and running you have a second radiator removing coolant heat in your overhead or dash depending where your evaporator is. If your system has a seperate heater core located in another area than your A/C evaporator than I apologize and none of this applies. My fan switch works independent of the A/C and I do not turn on the A/C while trying to heat the cab.

 

[kiotiken]

My opinion that most tractors have oversized cooling systems, unlike cars that must warm up quickly for emissions to drop. I rarely see them run hot under normal conditions. As long as coolant levels within range and radiators not completely clogged. That said it just takes a long time to warm up as they are so efficient at getting rid of engine heat. You might try the old trick of cardboard or plywood in front of the radiator to block airflow until the engine coolant is up to temp. When the A/C comp is engaged you are actually cooling the evaporator the same time as hot water is trying to heat the evaporator. The refrigerant is still flowing through the evaporator and cooling the hot water until it gets warm enough to overcome the refrigerant ability to cool. So with A/C engaged and running you have a second radiator removing coolant heat in your overhead or dash depending where your evaporator is. If your system has a seperate heater core located in another area than your A/C evaporator than I apologize and none of this applies. My fan switch works independent of the A/C and I do not turn on the A/C while trying to heat the cab.

Another big difference is cars and trucks now use electrically driven fans as opposed to the old belt driven system that tractors still use. Until there's heat in the system, your car or truck isn't blowing cold air through the rad so it'll warm up a lot faster. It's no wonder it take the coolant a while to come up to temp when it's -30C outside and you're blowing that cold air through the rad.

 

[ritcheyvs]

If the thermostat is working properly the radiator and fan should have very little effect. The main factor with Diesel engine warm-up is the amount of power produced. which is pretty small at idle. Gasoline engines, on the other hand, have to work to suck air past the throttle. Diesels don't have a throttle plate (there are rare exceptions) so the intake manifold is close to ambient pressure and the engine does minimal work on the intake stroke. The Russians have lots of cold weather experience and many of their Diesel vehicles include an oil heater and electric oil pump to lube the engine before attempting to start it. They also use compressed air for cold starts (injected on the power stroke) for many vehicles with an electric backup starter. I understand that it's best to warm up a Diesel with a light load (vs pure idle) after oil pressure is stabilized.

 

[SSdoxie]

Ken, Looking at the cab schematic for Bobcat (same cab) the voltage supply to the AC switch comes from the fuse, through the Hi/Low pressure switch. So if it is cold enough to reduce Freon pressure below minimum the switch won't receive power to light the indicator light. Or if Freon is low, needs a little re-charge.
The cab Evaporator is first inline of air flow from the blower fan, so cab air will have to be warm enough to blow warm air to the evaporator thermostat before compressor clutch engages. Not sure about the controls regarding internal recirculation vs. external air intake, but if it can be set to internal recirculate cab air the evaporator will warm up faster.

 

[Jose G]

you should not let the tractor sit on idle for a long period, let the throttle at 1k rpm if you have to.
it could wash the cylinder because of diesel burning poorly. does your oil smell diesel?
when I start my tractor, I normally let it idle for 5 mins at 0 throttle, then crank it up at 1k rpm to finish the warming process

 

[Jesse masterson]

My Dk 45 idles at 1 k. Always wondered of that was high.

 

[Looking4new]

My CK27 also idles at 1K. After the oil pressure is up I bump the throttle to 1200 and let her idle for 20 minutes or so before I get to work. I work (blow snow) right from the get go.

 

[irvingj]

Ken, I believe SSdoxie has it: I would also guess that there's a low-pressure shut-off-- many refrigeration systems have this.

Ambient temp around the evaporator coil would have to rise (tractor warms up) before internal refrigerant pressure would climb, LP would switch "ON" and allow compressor to run. The idea is to prevent the compressor from coming on (and possibly icing up the evaporator and/or sucking in air) if there's a leak and the refrigerant is low.

Also, keep in mind that if the evaporator does get iced up, refrigerant won't evaporate and there's a good chance of a slug of liquid getting back to the compressor…definitely not good. irvingj

 

[kiotiken]

Ken, Looking at the cab schematic for Bobcat (same cab) the voltage supply to the AC switch comes from the fuse, through the Hi/Low pressure switch. So if it is cold enough to reduce Freon pressure below minimum the switch won't receive power to light the indicator light. Or if Freon is low, needs a little re-charge.
The cab Evaporator is first inline of air flow from the blower fan, so cab air will have to be warm enough to blow warm air to the evaporator thermostat before compressor clutch engages. Not sure about the controls regarding internal recirculation vs. external air intake, but if it can be set to internal recirculate cab air the evaporator will warm up faster.

Ken, I believe SSdoxie has it: I would also guess that there's a low-pressure shut-off-- many refrigeration systems have this.

Thanks guys and sorry for the delayed response, just getting back into the swing of things after the holidays. I was out working with the tractor again last night. The temperature must have been colder than -30C, but I didn't check (who cares at that point). I fired up the tractor, waited a few minutes and idled it up to about 1200 RPM and switched on the PTO to get it warmed up. I also turned the cab air off to allow the heat to stay in the engine. After 20 minutes (at least) I came back out to the tractor and it was in the normal temp range so I turn on the heat, increase RPM up to about 1800 and slowly moved out of the shed. I then work the loader up and down a dozen times and scoop and dump the bucket as well, before going up to 2200-2400 RPM. It takes a lot to get everything moving properly at those temps. Anyway after about 10 minutes, my hat and gloves were off and the cab got quite warm. I worked for about 45 minutes total and then went to go put it away again. Right before killing the engine, I thought I'd try the A/C to see if it was working and sure enough, it was not.

So thank you for the explanation and checking the schematics for me. I will address it with my dealer in the spring before the warranty is up (I wouldn't let him float the tractor to his shop in the winter for anything be a total break down, there's way to much road salt). I'm thinking there must be a leak and the Freon level is low because there's no way that it should take that long to warm up. As cold as it was last night, the cab was toasty warm (and I'm assuming the ceiling space as well) and the engine was working hard and should have warmed everything else up in that time. I don't remember ever having this issue last year so something has changed.