M7-151 A/C question

[Spidermonkey11]

Morning all,

working on my neighbors M7-151, A/C quit. Went thru all of the diagnostics and found the compressor to be bad. So replaced the compressor and the tractor blew cold air for about 2 weeks. Now, the Low pressure and High Pressure read 100psi on both and the compressor won't kick on, obviously, because of it. Can anyone tell me where the expansion valve is located on this tractor? Is in under the floor? I've looked all around, not pulled the floor, and i must be blind.

thanks for the help

 

[Motion]

I'm not familiar with that tractor but if you at 100/100 with the compressor running then the new compressor may be bad. When replacing the compressor was the system properly flushed ( some condensers can't be properly flushed), was the dryer filter changed, was the correct amount and type of oil added, was the system brought down to at least 400 microns to ensure proper dehydration, was the exact charge of refrigerant added, are there any cab filters? Just my .02

 

[Spidermonkey11]

I'm not familiar with that tractor but if you at 100/100 with the compressor running then the new compressor may be bad. When replacing the compressor was the system properly flushed ( some condensers can't be properly flushed), was the dryer filter changed, was the correct amount and type of oil added, was the system brought down to at least 400 microns to ensure proper dehydration, was the exact charge of refrigerant added, are there any cab filters? Just my .02

Yep all of those processes were done to the correct specs, other than the dryer.

The pressure reading are with the compressor NOT running. Which, is more than likely, from the low pressure switch circuit being open.

Just seems odd to me that it ran fine for a few weeks without issue, and now it is not, which is why i was leaning toward the expansion valve.

 

[Motion]

Anytime a system is open, it's good practice to change the filter dryer. With 100# suction the low pressure switch should be made and allow the compressor to come on, although briefly. when it cuts out and the system is equalizing is there a temperature / pressure difference across the filter dryer? If the original compressor blew the first stop for trash is the condenser, second stop is is the filter dryer. Not sure what type condenser you have but parallel flow condensers can't be flushed.

 

[Spidermonkey11]

Anytime a system is open, it's good practice to change the filter dryer. With 100# suction the low pressure switch should be made and allow the compressor to come on, although briefly. when it cuts out and the system is equalizing is there a temperature / pressure difference across the filter dryer? If the original compressor blew the first stop for trash is the condenser, second stop is is the filter dryer. Not sure what type condenser you have but parallel flow condensers can't be flushed.

10/4 on the dryer. I have had a fair amount of success without replacing the dryer, but there is always a first.

I unplugged the compressor clutch to see if there was power going to it to engage and during the 10 minutes of running and the pressures staying at 100, the pressure switch never closed to provide power to engage the clutch.

In regards to the condenser, i will need to take a look at it to determine the manufacturer/flow type.

 

[Motronic]

10/4 on the dryer. I have had a fair amount of success without replacing the dryer, but there is always a first.

Replacing the dryer isn't what makes or breaks your repair immediately. The function of the dryer is to remove the last bits of moisture in the system after you close it back up. If there isn't a new dryer installed to do that the water turns the refrigerant acidic and the system is eaten from the inside out. How fast? A year? 10 years? Depends on exactly how much water was left in the system/how low and for how long you vaced it.

 

[Spidermonkey11]

Replacing the dryer isn't what makes or breaks your repair immediately. The function of the dryer is to remove the last bits of moisture in the system after you close it back up. If there isn't a new dryer installed to do that the water turns the refrigerant acidic and the system is eaten from the inside out. How fast? A year? 10 years? Depends on exactly how much water was left in the system/how low and for how long you vaced it.

I ordered a replacement dryer and expansion valve. I'll see what i see when i open her up, again...

 

[Motion]

To run the compressor for 10 minutes, I assume you put 12 volts to the compressor clutch. With100/100#'s you're not moving any gas. Check the wiring diagram and see what other safeties or operating controls is not allowing the clutch to pull in. Changing the filter dryer isn't going to do any good at this point, you need a compressor and start over. Does this system have an expansion valve or an orifice tube?

 

[Spidermonkey11]

To run the compressor for 10 minutes, I assume you put 12 volts to the compressor clutch. With100/100#'s you're not moving any gas. Check the wiring diagram and see what other safeties or operating controls is not allowing the clutch to pull in. Changing the filter dryer isn't going to do any good at this point, you need a compressor and start over. Does this system have an expansion valve or an orifice tube?

Yep, starting over. Ordered everything today and going to go thru it this weekend. Compressor/dryer/evap/expansion valve/ etc...

 

[lugbolt]

what was wrong with the compressor? Did you take it apart?

Typically compressors, if they die internally (scroll compressors especially) they'll distribute debris throughout the entire system. If that happens (and it usually does if the compressor is actually dead), you will likely have better success replacing anything that the refrigerant touches. Basically every single part, hoses and all. If not, there's a higher probability of a comeback, meaning any debris that gets lodged in the condenser evaporator hose(s) txv, whatever, will get to the compressor again and destroy the new compressor. With that said, scroll compressors (and kubota uses a lot of them) are particularly sensitive to junk in the system--and that includes moisture.

secondly if the system is not charged properly and/or the evaporator gets plugged, there's possiblity that liquid refrigerant made its way back to the compressor. Compressors don't compress liquids. They self-destruct. It's not all that common but it can happen.

 

[dvcochran]

Yep, starting over. Ordered everything today and going to go thru it this weekend. Compressor/dryer/evap/expansion valve/ etc...

When the system on my M9 went out it was a hard rule that it is impossible to flush the style of condensers Kubota (and others) use now a days. Was told to definitely change the condenser if the compressor had failed.
When I did mine I replace compressor, condenser, expansion valve, and dryer. The new exp. valve went bad after about 2 weeks and had to be replaced.
Also, I had a Hard time getting all the flush out. I wish I have never flushed the system and just blown everything out with compressed air and then flushed with nitrogen.

 

[Motronic]

When the system on my M9 went out it was a hard rule that it is impossible to flush the style of condensers Kubota (and others) use now a days.

Parallel flow. And yeah, you can try to flush them but it never really works out. Best to just scrap them and start over so you don't end up trashing another compressor.

 

[wgator]

Any time you open a systen, once repairs are complete and everything is installed, you have to pull a vacuum to remove any moisture. Close gauges and let the vac set for a few hours to insure it holds meaning no leaks. If no leaks then recharge. If you don't pull vacuum, you will have moisture in system leading to failures in the future even with new filter/dryer.

 

[Motronic]

Any time you open a systen, once repairs are complete and everything is installed, you have to pull a vacuum to remove any moisture. Close gauges and let the vac set for a few hours to insure it holds meaning no leaks. If no leaks then recharge. If you don't pull vacuum, you will have moisture in system leading to failures in the future even with new filter/dryer.

This is a good point......my comments were assuming everyone knew this part as well. They dryer is for what you don't get out on the vac.

 

[Jim L.]

R134a makes for a new practice. The oil used with this refrigerant sucks up water and moisture, forming acid. Current practice is a triple evacuation, with dry nitrogen to break vacuum each time. Evacuation by itself will not pull moisture from the new oils. This is the job of a new dryer/filter.

Any torch work requires flowing low pressure nitrogen while brazing. Otherwise, the black gunk produced in the tubing will clog up the expansion device.