JD 3720 Air Conditioning line pressures?

[JDneophyte]

with your system running what does your head pressure climb to before tripping out? when the unit is not running your pressures should eqallize and be the same on both sides of the system. i dont believe its a plug in the system, but not able to get rid of the heat in the condenser. not sure how your system is set up but do you have an independant condenser fan

I think it was about 350 (not 100%, but the gauge maxes out at 500psi....and it was about 3/4's of the dials range). What makes me believe it's a plug is after starting......the low side stays at 50 PSI . the high side quickly climbs....then cuts out. Can't think of what else would do that.

System is clean (condensor, filter). The temp out of the vent is ambient.....no change.

 

[JDneophyte]

Why do you tease me? It was 96 degrees.....and had to open both doors and rear (now try keeping the right door open while driving).

The temperature was ambient with A/C on......no change.

 

[jenkinsph]

I think it was about 350 (not 100%, but the gauge maxes out at 500psi....and it was about 3/4's of the dials range). What makes me believe it's a plug is after starting......the low side stays at 50 PSI . the high side quickly climbs....then cuts out. Can't think of what else would do that.

System is clean (condensor, filter). The temp out of the vent is ambient.....no change.

When you say the "System is clean (condenser,filter) do you mean the evaporater coil and filter above the headliner? While these need to be clean most problems have been with the condensor coil mounted in front of the radiator. This condersor coil needs to be kept very clean. Can't stress this enough.

 

[JDneophyte]

Thats correct. I spent a good amount of time on the forums before posting (a plethora of knowledge) looking for most common issues. I even checked for air leaks in the cab roof (as we have a stereo installed).

 

[sandman2234]

Never mind, already mentioned...
David from jax

 

[jenkinsph]

Thats correct. I spent a good amount of time on the forums before posting (a plethora of knowledge) looking for most common issues. I even checked for air leaks in the cab roof (as we have a stereo installed).

You would think that if the high side pressure is running high enough to shut itself down and you are positive the condenser is clear of any debris that you may have something blocking the line. But you have the 50 psi on the low side, I would expect this to drop if the gas wasn't getting thru the evaporator. You also state that the air passing over the evaporater coil is ambient temperature. So to me you aren't getting the heat removed from the condenser.

I work primarily with R22 and Puron systems which have different characteristics but I suspect you need to take your tractor in for a complete vaccum and recharge with a well trained technician. It is hard enough to troubleshoot in person muchless over the internet.

 

[sunnyside360]

I had similar problem with my cab tractor and found a mobile technician who came to my house to diagnose and fix it. This was less costly than transporting the tractor to/from the dealer. Problem turned out to be a loose electrical connection on a switch (high pressure?) in the roof cavity. A real bugger to find and cost me $125 plus got a 90 day warranty. Considered it money well spent. You might consider doing the same.

 

[hizoot]

Ill lay money on that You've got a plugged condenser. If it was a restriction the high side will climb and the low side will drop and even go into a vacuum. I had a fellow call me one time with the same complaint. He swore the condenser was clean, and it did look it. But I took the battery out from in front of it loosened the coil. It was a double row coil and had all kind of trash in the middle you could not see .... do the same with yours. Powerwash that coil. Just make sure the wAter stream goes straight into the fins to keep from bending them.
This all presumes it has been running right before and no one has overcharged it

 

[jenkinsph]

Ill lay money on that You've got a plugged condenser. If it was a restriction the high side will climb and the low side will drop and even go into a vacuum. I had a fellow call me one time with the same complaint. He swore the condenser was clean, and it did look it. But I took the battery out from in front of it loosened the coil. It was a double row coil and had all kind of trash in the middle you could not see do the same with yours. Powerwash that coil. Just make sure the wAter stream goes straight into the fins to keep from bending them.
This all presumes it has been running right before and no one has overcharged it

''\


He mentionsed on page 1 that he added a can of freon. What I suspect has happended is the condenser is plugged enough to reduce the effectiveness of the system then he added a can of freon and it is now overcharged and still has the plugged condenser. It is shutting down to protect itself.

I would remove an equal amount of freon to match what was put in by JDneophyte, clean the condenser with an acid wash throughly then see what the guages show.

 

[hizoot]

Thanks Steve..I missed that as I was posting from my iphone. Looks like I missed a bunch of punctuation in my post as well:laughing:. I agree, its probably overcharged now....and will need the coil cleaned too.

Funny story: I've been doing HVAC work now for 34 years and own airtechtyler.com . My mothers car was not cooling as it should...well she didnt want to bother me since I was having long days and no days off . Her boyfriend said...."It just probably needs some freon" So he proceeds to put in 4 cans as one wasnt doing it...nor 2,etc.. Of course now it wouldnt cool at all. So, I drive 50miles to her house that evening,recapture all the refrigerant and cleaned her condensor coil that was full of mayflies. It seems the first thing people think of when a unit isnt cooling is "low on freon". But...I was the same way before getting into this stuff.