zdman
Member
The AC is not working properly in the cab. Seems to run and blow cold air for a while, but then the air coming out is only a little cooler than outside air temp. Seems to do the same whether in fresh air or recirculate mode. Any ideas?
1736 Premium Cab - ac working intermittently
- Thread starter zdman
- Start date
- Views: 5372
jeepcj7
Platinum Member
- Joined
- Oct 18, 2004
- Messages
- 601
Could be evaporator freezing up.
Doug62
Silver Member
I've noticed my 1835M not cooling as well after I've used it heavily for a while. I think under heavy loads the compressor might be shutting off like it does on a car when you accelerate hard.
lpakiz
Gold Member
- Joined
- Jul 25, 2017
- Messages
- 430
- Location
- Greenwood, WI
- Tractor
- MF1754 HST, Cab, 6 foot Front Mount Snowblower
I’m just guessing here, but could you watch the drain hose, from under the evaporator, for water drops? Mine (and most vehicles with AC) drip pretty heavily in muggy weather.
If it drips good at first, then stops dripping, it might be icing/freezing up.
Or when you shut down, put a catch-can under that drain hose. If it gets some water in it after a 1/2 hour of not operating, that could be ice blocking the evaporator coil, then melting and running out.
A plugged cabin air filter could be the culprit, and on trucks, we used to run into a faulty blend/mix door or actuator not allowing enough air thru the evap to keep up with the cold you are making.
If it drips good at first, then stops dripping, it might be icing/freezing up.
Or when you shut down, put a catch-can under that drain hose. If it gets some water in it after a 1/2 hour of not operating, that could be ice blocking the evaporator coil, then melting and running out.
A plugged cabin air filter could be the culprit, and on trucks, we used to run into a faulty blend/mix door or actuator not allowing enough air thru the evap to keep up with the cold you are making.
I did check the cabin filter (is on outside of the cab under roof lip) and it was fine. I did watch and am not seeing any water coming out or the drip hose. Normally there is a lot coming out after ac has been running. I need to find out where the connector is to measure and add Freon.
lpakiz
Gold Member
- Joined
- Jul 25, 2017
- Messages
- 430
- Location
- Greenwood, WI
- Tractor
- MF1754 HST, Cab, 6 foot Front Mount Snowblower
Unless you’re sure it’s low, adding Freon doesn’t mean more or colder air. If you have good air flow from the ducts, check the compressor to see if the clutch is turning the center hub. The clutch is controlled by several pressure switches in series. If the compressor is indeed running, the bigger of the 2 pipes going into the compressor (suction pressure) should be pretty cold, and the small one should be quite a bit warmer.
If I suspected a sensor, I would hot wire the clutch (careful here, hope you know what you’re doing) and see if cold air was produced. If this resulted in adequate cold air, there’s nothing wrong with the mechanics of the system, including freon level, belt tension, plugged evap or condenser, etc.
The problem is in the switches controlling the clutch.
This might be the time to call for reinforcements…….
If I suspected a sensor, I would hot wire the clutch (careful here, hope you know what you’re doing) and see if cold air was produced. If this resulted in adequate cold air, there’s nothing wrong with the mechanics of the system, including freon level, belt tension, plugged evap or condenser, etc.
The problem is in the switches controlling the clutch.
This might be the time to call for reinforcements…….
metalbender
Veteran Member
Airflow through condenser good??? Clean the screens at the front.
thclimer
Veteran Member
Thanks for letting us know you fixed it.
lpakiz
Gold Member
- Joined
- Jul 25, 2017
- Messages
- 430
- Location
- Greenwood, WI
- Tractor
- MF1754 HST, Cab, 6 foot Front Mount Snowblower
For the benefit of the next person who has similar AC symptoms, check back on my earlier post (7) where I mentioned that the compressor is controlled by several switches "in series." One of those switches is to prevent "over-pressure" which could blow out hoses, condensers or even damage the compressor. (Another switch senses freon pressure "at rest" and won't let the compressor run if the system doesnt have adequate freon, like if it's all leaked out)
What was probably happening here is that when the operator first turned on the AC, the compressor started normally, but since the freon wasn't being cooled down enough, pressure went up and beyond the "over-safe-pressure" limit, so that switch opened. After a time, when the freon pressure eventually fell, that switch closed and the compressor ran again, for a while, until pressure again got too high. The cycle repeats until the cause of the excess pressure (plugged condenser) was corrected.
There is another control switch that senses pressure at the evaporator core in the heater box in the cab. That switch tells the compressor to shut off if the pressure (temperature) is too low (too cold). It may be part of the temperature controls in the cab.
If the low pressure fall too low (too cold) this switch prevents damage and also prevents humidity from freezing up on the evap core into a solid block of ice, resulting in no air flow thru itself.
Also, if air flow thru the evap core is too low because of a failed blower switch or a plugged up cabin air filter, or doors in the duct system not being in the correct position, this switch shuts off the compressor to prevent the evap from icing up. If this switch fails to shut off the compressor, ice can build up on the core. Shutting off the tractor and placing a can under the drain hose will catch this ice as it melts, indicating this condition. That's why adequate air flow out of the cab ducts is important--the air flow must carry the "cold" out of the evaporator core as fast as it's produced, or freeze up results.
Oh, in addition to all these control switches, all the related connections and wires and fuses and every other component in the system must be intact, or no cold air. Hot wiring the compressor temporarily bypasses all these controls to help diagnose the problem. If hot wiring the compressor clutch produces cold air, the mechanics of the system are OK, and the problem is electrical, usually.
And sometimes the system not only interrupts the electrical supply to the clutch, but in some cases, it can also interrupt the ground. If the compressor clutch has 2 terminals, hot wiring could include directly grounding the ground terminal. You must know which is which, or you will blow a fuse.
What was probably happening here is that when the operator first turned on the AC, the compressor started normally, but since the freon wasn't being cooled down enough, pressure went up and beyond the "over-safe-pressure" limit, so that switch opened. After a time, when the freon pressure eventually fell, that switch closed and the compressor ran again, for a while, until pressure again got too high. The cycle repeats until the cause of the excess pressure (plugged condenser) was corrected.
There is another control switch that senses pressure at the evaporator core in the heater box in the cab. That switch tells the compressor to shut off if the pressure (temperature) is too low (too cold). It may be part of the temperature controls in the cab.
If the low pressure fall too low (too cold) this switch prevents damage and also prevents humidity from freezing up on the evap core into a solid block of ice, resulting in no air flow thru itself.
Also, if air flow thru the evap core is too low because of a failed blower switch or a plugged up cabin air filter, or doors in the duct system not being in the correct position, this switch shuts off the compressor to prevent the evap from icing up. If this switch fails to shut off the compressor, ice can build up on the core. Shutting off the tractor and placing a can under the drain hose will catch this ice as it melts, indicating this condition. That's why adequate air flow out of the cab ducts is important--the air flow must carry the "cold" out of the evaporator core as fast as it's produced, or freeze up results.
Oh, in addition to all these control switches, all the related connections and wires and fuses and every other component in the system must be intact, or no cold air. Hot wiring the compressor temporarily bypasses all these controls to help diagnose the problem. If hot wiring the compressor clutch produces cold air, the mechanics of the system are OK, and the problem is electrical, usually.
And sometimes the system not only interrupts the electrical supply to the clutch, but in some cases, it can also interrupt the ground. If the compressor clutch has 2 terminals, hot wiring could include directly grounding the ground terminal. You must know which is which, or you will blow a fuse.
Last edited:
Doug62
Silver Member
Good info to have for cab owners. My AC was acting similarly last year and cleaning the screen also helped it cool better.
Here are some similar links:
