A/C help again

Finally starting to make some progress on the A/C project in the tractor. Again its a R12 system converted to 134. The compressor seems to be fine after I overcharged it the first time. Now I am working smarter adding it with the guages and as vapor.

Currently have about 36 ounces in the system and its still low. The sight glass still shows air bubbles and the low side pressure is only 15 the most I have seen so it cools good but will freeze the evap coil like that.

The real problem though is the high side pressure is up to 190 on a 70 degree day. Checked the condensor coil and its clean.

So what gives what could cause the high side to be so high like that and the low side so low?

1.) Did you evacuate the system with a vacuum pump before charging?

2.) The condenser depends upon airflow for cooling. How fast was the engine running when you were seeing the high-side pressures approaching 200 PSI?

3.) If you add R-134 'til the sightglass is clear (like we used to with R-12) the system will be OVERCHARGED with R-134.

Yes I did evacuate the system before charging.

Engine RPM was 1600 with enough airflow to blow my hat off my head.

Thanks for the tip on the sightglass. Didn't know that one. But either way the low pressure side is too low and could see it on the line going to the cab as it was icing up.

Seems simple but there has to be something I am missing and I am no A/C expert.

I was told not to exceed 150 psi when charging a system and pushed it a little hoping it would stabilize and come down. But after running it a good 15 min after adding refrigerant it didn't come down any.

In the cab I was getting 12-13 degree drop in temp from fan inlet to outlet

Bill,

Don't know what yer working on, but standard rule of thumb is that if the low side is too low and the high side is too high, she's plugged up somewhere.

Things aren't moving as they should.

If this system uses an orifice tube, I'd sure look at that filter.

If on the other hand, if it has an expansion valve, check the capillary to make sure it is in place; also good air movement thru the evaporator.

Tractors are famous for muddin' up the evaporator and the capillary can't read the system to control flow.

Allan

Bill,

Are you working on the 1066?

I guarantee you that condenser and evaporator are both plugged tight with mud if ya haven't already cleaned 'em.

Also, just another tip: :>)

On IH tractors, you absolutely HAVE to have that gasket in place under the roof panel. It will not work right if it leaks air.

Allan

Do a Google search for jbabs. Just type in jbabs. It is a site that explains air conditioning systems and has helped me many times.
Let me know if you have trouble finding this site.

You PROBABLY have so many variable here that it defies imagination

First, is this an existing system THAT WORKED WELL?

Second, you are doing a refrigerant conversion. Think in terms of gas versus diesel. R134 is NOT R12

ARE YOU SURE, ABSOLUTELY SURE that you have enough fan past the condenser? (Might try a big 110V fan if you have one to move more air)

Anytime you make changes in a refer system (refrigerant change) , you can affect the whole system.

It's possible that the high side is too high because it is OVERCHARGED and the liquid is reducing the condenser capacity. An overcharge can fool you---there may be SOME OTHER CAUSE for the low side pressure that is making you think the charge is low, so you just kept adding refrigerant.

Low low side: Not enough evap fan--dragging motor, plugged evap/ filters/ dirty blower, etc

Plugged, undersized or WRONG expansion valve. You might check if you need to get a different TXV (if used) for R134 for your application YOU MAY simply have a Txv or other low side metering device going bad on you.

Correct on the sightglass. I don't even know why manufacturers install them. I'd charge slowly and watch the pressures and temp, and monitor compressor superheat. I'm not familiar with R134, but I used to use a rule of thumb of NOT LESS than 20*F compressor superheat. Be sure to check this with the sensor wrapped with insulation, as engine heat will affect your readings The LAST thing you want to do is slug the compressor with refrigerant

Air, water, or other "non condensibles" in this system can cause high side pressure, but WATER even very little can freeze up and plug up the metering device. I DOUBT that ice/ water is your problem--this usually comes and goes as an idle system will allow the plug in the metering device to melt over idle periods

Was this system "left open" for a period of time? Did you change (or does it have) a filter/ dryer?

What happens when you add more freon ? Most car and truck systems run 250-350 on the high side . I don't have much experiance with ag systems, but I'd think they should be close ?
I'd add freon till it hits 350 ,make sure you have good air flow across condensor , see what happens .

"Currently have about 36 ounces in the system and its still low. The sight glass still shows air bubbles and the low side pressure is only 15 the most I have seen so it cools good but will freeze the evap coil like that."

You may be overcharged with those pressures on a 70 degree day using R134a. 15 psi low side is not out of line with 70 degree air temp, 190 on a 70 degree day is border line high (rule of thumb is 2---2-1/2 times air temp is normal high side pressure.

NEVER EVER use the sight glass to determine charge level when charging a converted system with R134a. Little globules of Ester oil floating in the refrigerant looks exactly like bubbles. If you have a clear site glass running R134a, you are very overcharged, which would explain the higher high side pressure.

What works best for me is to add just enough R134a to get the system cooling and add more, 2 oz at a time until a vent thermometer shows no drop in vent temp with the addition of a couple more oz of refrigerant. STOP at that point, that is the sweet spot that will produce maximum cooling in a converted system with minimum high side pressure. Adding more can actually decrease cooling and high side pressure goes crazy high.

(quoted from post at 10:04:13 05/06/09) What happens when you add more freon ? Most car and truck systems run 250-350 on the high side . I don't have much experiance with ag systems, but I'd think they should be close ?
I'd add freon till it hits 350 ,make sure you have good air flow across condensor , see what happens .

Click to expand...

I find that pretty hard to believe. Looking at the R134 chart

http://dodgeram.org/tech/repair/HVAC/R134a.htm

somewhere around 250 psi equates to a condensing temp of 150 degrees!!!

In this part of the woods, for example, on rooftop commercial units, I was used to seeing R22 heads below 300PSI which equates to 130*F or so condensing, and that's on a hot day, not 70F ambient

Brain farts in my head yet . Not into the heat of summer . Ment to say or babble . High side around 250, , some peak to 300 , before fans kick on . But,,on most conversions i see steady 250 high side .

A plugged expansion valve will NOT cause high high side pressure. It causes low pressures on both sides. If there is little refrigerant getting into the evaporator, the compressor doesn't have anything to work with and therefore the low side goes very low and the high side is also low because very little heat is created. 10 to 15 psi is normal on TXV systems that use a thermostatic switch to control compressor operation.
When I retrofit to 134, I start with 50% of the R12 capacity and do much like Jon does.

No its not a 1066. We gave up on the air in that one long ago. Its on a 4840 massey and the system in this thing is huge. The condensor is clean but still have to verify the evap coil but it does have strong air flow out the vents.

I have watched the system fill from 30 inches of vaccum to now 20 psi on the low side all went in as vapor from small 12 oz cans. We are up to 96 ounces and still wondering what the heck. Low side is 20 high side 220. The filter in the system isn't sweating any so it shouldn't be plugged. I know about enough about A/C systems to be dangerous but trying to learn.

Thinking if it don't rain will be in the fields tomorrow for the first time this year and just going to run it and see how it works for now.

Hello Bill in Il,
Your system is low on refrigerant. The best way to get the correct amount in the system, is like i told you on my last post.
Temperature(OUT OF THE AIR VENT) and pressure.
R134A carries a lot more pressure then R12.
If you can put a thermometer at the end of the evaporator while charging, it will tell you when it stoppes getting cold. What temperature are you getting out of the air vents? Any temperature below 50 Degrees is good, if you are not getting at least that, you are not close of having a full charge.
Guido.