Air conditioner issue

KenOverton · Jul 17, 2016

Working on my neighbor's 2000 dodge ram 1500. I'll explain in short detail the issues leading up to the problem. Truck sat for approx. 2 years with a bad motor. Swapped in a good motor from a donor truck, AC was de-serviced during motor swap, but parts reconnected to keep out dirt/moisture. Truck has been driven for just over 2 years without servicing the AC. Yesterday we swapped in a new high pressure service line (with fixed orifice), new receiver dryer, flushed evaporator and condenser, drained oil out of compressor and serviced with fresh oil. After servicing Freon the low side line from compressor through the receiver dryer up to firewall is freezing up, and there is no cooling air inside the truck (air is hot). Low side pressure is about 15 PSI running idle, high side is approx. 185 psi. Above 1500 rpm low side returns to 0 psi, high side has no change.
I am leaning toward a bad compressor, but I hate to have him buy a new compressor if the problem may be somewhere else. If some could help us out I would be very grateful.

Ken

auskip07 · Jul 17, 2016

Did you pull a vacuum on the system before you filled it? If not you have moisture in the air and in the system causing it to freeze (i know you said you tried to keep dirt and moisture out but if you opened up the system moisture is in the air

KenOverton · Jul 17, 2016

auskip07 said:
Did you pull a vacuum on the system before you filled it? If not you have moisture in the air and in the system causing it to freeze (i know you said you tried to keep dirt and moisture out but if you opened up the system moisture is in the air

Of course I pulled a vacuum. No leaks either. Wouldn't have wasted the money on new parts otherwise..

How could you service without pulling vacuum?

auskip07 · Jul 17, 2016

KenOverton said:
Of course I pulled a vacuum. No leaks either. Wouldn't have wasted the money on new parts otherwise..

How could you service without pulling vacuum?

Ive seen it done. Not recommended either

dudeman2009 · Jul 18, 2016

15psi idle seems way low to me, it should be above 30 at idle and drop to compressor cutoff around 25psi under accel or high reving. High side could be anywhere from 180 to 350psi, I cant remember what it is on this generation of dodges.

Add freon at idle while the compressor is running until the low side is 25-35 at 65F 35-40psi at 70F, 75F is 35-45, 80F is 40-50, 85-90F is 45-55.

crash68 · Jul 18, 2016

If you weighed in the refrigerant charge and with your low side @15psi your compressor shouldn't be running(low pressure switch) and if you high side doesn't go up(with the low side dropping) when you give it more rpms, sounds like you might have a restriction. Check your low side gauge for accuracy also.

KenOverton · Jul 18, 2016

crash68 said:
If you weighed in the refrigerant charge and with your low side @15psi your compressor shouldn't be running(low pressure switch) and if you high side doesn't go up(with the low side dropping) when you give it more rpms, sounds like you might have a restriction. Check your low side gauge for accuracy also.

After adding the first 12oz I bypassed the pressure switch to prevent the compressor cycling. Total charge in the system is about 36oz, last 12oz added very slowly. Label says qty should be 32oz, so at some point before the third can was empty it should have started working, and now pressures should be high, not low. If I remove the jumper on the pressure switch, the compressor cycles at about 3-5 seconds on, then off about the same.

Would the restriction be in the evaporator? Never seen one blocked unless the compressor failed and filled with particles from that. This one did not fail in that way.

When flushing, it seemed more restricted than the one on my car when I had to replace the compressor and condenser on it, but I wasn't sure on the design on the dodge. The only AC book I can find, and I have one, was probably written 15 years ago.

Gauges are accurate. I took my car to a shop to verify that the NEW expansion valve I installed was bad, and their gauges read the same as mine.

crash68 · Jul 18, 2016

KenOverton said:
Would the restriction be in the evaporator? Never seen one blocked unless the compressor failed and filled with particles from that. This one did not fail in that way.

When flushing, it seemed more restricted than the one on my car when I had to replace the compressor and condenser on it, but I wasn't sure on the design on the dodge. The only AC book I can find, and I have one, was probably written 15 years ago.

I'm not sure whether Dodge uses an evaporator with a single or multiple circuits. I am guessing the latter and possible the distribution tubes/header is plugged or possibly even your new flow orifice. You may even want to check that the orifice tube is correct one.
I reread your first post, didn't pick up on the frost line you have. Follow that back to the restriction.

KenOverton · Jul 18, 2016

crash68 said:
I'm not sure whether Dodge uses an evaporator with a single or multiple circuits. I am guessing the latter and possible the distribution tubes/header is plugged or possibly even your new flow orifice. You may even want to check that the orifice tube is correct one.
I reread your first post, didn't pick up on the frost line you have. Follow that back to the restriction.

Orifice is located in the high pressure line between the condenser and evaporator, not sure how you can verify that it is not restricted, or if it the correct one. Can't see it, ordered by year and model.

Frosted line is between the compressor and evaporator (low press side). From what I can understand from the AC book I have, the frozen line would be just after the restriction. So, under normal operation the line after the orifice tube would be cold (not frozen) Am I thinking correctly? That would mean the restriction is in the evaporator?

Just want to be sure before buy more parts.

crash68 · Jul 18, 2016

KenOverton said:
Frosted line is between the compressor and evaporator (low press side). From what I can understand from the AC book I have, the frozen line would be just after the restriction. So, under normal operation the line after the orifice tube would be cold (not frozen) Am I thinking correctly? That would mean the restriction is in the evaporator?

The restriction is about or just before where the frost line starts, it could be in the evaporator. It maybe in the distribution header of the evaporator. You usually can buy and replace just the orifice tube, maybe check the dealer for sizing/correct part. They are usually located right the connection at the inlet of the evaporator. Open up the system and back flush/blow out(backwards) the evaporator with nitrogen and inspect the orifice tube. Check the receiver/drier if any loose particles come out of it.

KenOverton · Jul 18, 2016

crash68 said:
The restriction is about or just before where the frost line starts, it could be in the evaporator. It maybe in the distribution header of the evaporator. You usually can buy and replace just the orifice tube, maybe check the dealer for sizing/correct part. They are usually located right the connection at the inlet of the evaporator. Open up the system and back flush/blow out(backwards) the evaporator with nitrogen and inspect the orifice tube. Check the receiver/drier if any loose particles come out of it.

As I stated above, the orifice is located in the high pressure service line, between the condenser and the evaporator, and it has been replaced. It is not replaceable other than changing the complete line. I have already flushed the evaporator, and my concern was that it did seem restricted compared to the condenser on my Mazda 3 and my wife's Mazda 6 she had a while back, which are the only ones I can compare it to. Receiver dryer is new also.

Frost starts at firewall coming out of the evaporator. Cant tell if evaporator is frozen up due to location.

If what you are telling me is that there should be no restriction in the evaporator, then that answers my question.

But, if that is the case why is the high side pressure low, does that mean a bad compressor also? I am thinking both are bad, but hate throwing money at a problem. Would rather have more info, especially since it is not my truck. If it was mine, I would replace both.

crash68 · Jul 18, 2016

KenOverton said:
Frost starts at firewall coming out of the evaporator. Cant tell if evaporator is frozen up due to location.
If what you are telling me is that there should be no restriction in the evaporator, then that answers my question.
But, if that is the case why is the high side pressure low, does that mean a bad compressor also? I am thinking both are bad, but hate throwing money at a problem. Would rather have more info, especially since it is not my truck. If it was mine, I would replace both.

not familiar with the AC system in this truck but all refrigeration systems react pretty much in the same way. If the orifice is in that line, when the system is running it will start getting cold after the restrictor, if that part of the line is warm, your restriction is after that point which points at the evaporator. A cable cam would help in seeing the evaporator. The evaporator looks like(from a picture) a micro channel style, there will be some resistance but the frost line is the tattletale sign.
I don't think the compressor is bad, once all the refrigerant is pumped into the condenser/drier and now evaporator(cause of the blockage), it can't absorb heat/flow properly and will only build so much pressure. Adding more refrigerant to the system now would cause the head pressure to spike high with a low suction pressure.

dudeman2009 · Jul 18, 2016

As crash stated, wherever the line starts getting cold is where the the blockage is.

What was the ambient temp, that is important to know, at 100F you should have 270-330PSI, at 70F its only 135-145PSI. So trying to determine if the compressor is bad or if its just low on refrigerant is impossible.

If it was 90F out like it was here in Michigan the past week, then your just don't have enough refrigerant in it.

You are right to assume that the section right after the greatest restriction. There may rarely be ice on the outside of the line as well, but usually it's just a bunch of condensation.

Also the test is to be performed at 1000rpm, bypass the low side pressure switch as you already have. Note ambient temps must be at least 70F. Since the air coming from the A/C vents is warm, just for kicks, clamp off both heater hoses in the engine bay and check the air temps in 5 minutes. If that doesnt help then move on to the next part.

Record the ambient temperature and both high side and low side temps. From there we can narrow it down to a couple things instead of stabbing in the dark. Above 1000 rpm the compressor will cycle much more often as its speed is increasing its ability to compress refrigerant. Pressure dropping to 0PSI above 1500rpm with the low side switch bypassed is expected, if it didn't drop i'd say the compressor is bad.

KenOverton · Jul 19, 2016

dudeman2009 said:
As crash stated, wherever the line starts getting cold is where the the blockage is.

What was the ambient temp, that is important to know, at 100F you should have 270-330PSI, at 70F its only 135-145PSI. So trying to determine if the compressor is bad or if its just low on refrigerant is impossible.

If it was 90F out like it was here in Michigan the past week, then your just don't have enough refrigerant in it.

You are right to assume that the section right after the greatest restriction. There may rarely be ice on the outside of the line as well, but usually it's just a bunch of condensation.

Also the test is to be performed at 1000rpm, bypass the low side pressure switch as you already have. Note ambient temps must be at least 70F. Since the air coming from the A/C vents is warm, just for kicks, clamp off both heater hoses in the engine bay and check the air temps in 5 minutes. If that doesnt help then move on to the next part.

Record the ambient temperature and both high side and low side temps. From there we can narrow it down to a couple things instead of stabbing in the dark. Above 1000 rpm the compressor will cycle much more often as its speed is increasing its ability to compress refrigerant. Pressure dropping to 0PSI above 1500rpm with the low side switch bypassed is expected, if it didn't drop i'd say the compressor is bad.

Sorry I thought I put the temp in. Here in middle GA the ambient temp was 95+ on Saturday. High pressure line after the orifice does not get cold. Line between the evaporator including the dryer all the way to the compressor is iced up, not just condensation.

Freon serviced into system is 36oz plus. Added a couple of ounces after 3 cans just trying to get pressures to go up, so I am sure there is enough Freon in the system.

Thanks for all the help. I will let everyone know what happens after this weekend. Discussed with my neighbor and he has ordered a new evaporator and compressor.

dudeman2009 · Jul 19, 2016

KenOverton said:
Sorry I thought I put the temp in. Here in middle GA the ambient temp was 95+ on Saturday. High pressure line after the orifice does not get cold. Line between the evaporator including the dryer all the way to the compressor is iced up, not just condensation.

Freon serviced into system is 36oz plus. Added a couple of ounces after 3 cans just trying to get pressures to go up, so I am sure there is enough Freon in the system.

Thanks for all the help. I will let everyone know what happens after this weekend. Discussed with my neighbor and he has ordered a new evaporator and compressor.

Being 95, those pressures are way to low. That indicates that the compressor is pulling a vacuum, i'd guess that your evaporator is clogged, the service manual lists either the evaporator or accumulator is reducing coolant flow. That would result in low pressures all around given a proper 32oz charge.

KenOverton · Jul 19, 2016

dudeman2009 said:
Being 95, those pressures are way to low. That indicates that the compressor is pulling a vacuum, i'd guess that your evaporator is clogged, the service manual lists either the evaporator or accumulator is reducing coolant flow. That would result in low pressures all around given a proper 32oz charge.

These were my thoughts also. With the high side being low, could this be because of the evaporator? My understanding says that the compressor is faulty also.

I do appreciate all the assistance.

crash68 · Jul 19, 2016

KenOverton said:
With the high side being low, could this be because of the evaporator? My understanding says that the compressor is faulty also.

If the compressor is pulling down to zero/into a vacuum, it is probably safe to say the compressor is not bad.
With the evaporator plugged/restricted, it can cause the lower pressure on the high side, with the low/no suction pressure, there is less refrigerant for the compressor to pump and build pressure on the high side.

dudeman2009 · Jul 19, 2016

KenOverton said:
These were my thoughts also. With the high side being low, could this be because of the evaporator? My understanding says that the compressor is faulty also.

I do appreciate all the assistance.

The high side builds pressure only becuase there is a limited volume before it hits the primary restriction, the expansion valve in the liquid line. However, should that restriction be moved down the line, the total volume before the liquid expands is much greater, meaning that more R134 can be compressed without an increase in pressure, since there is more r134 compressed after the compressor, there will be less on the suction side of the compressor.

I would say your compressor is good if it was 95F out, that would indicate that there is low pressure all around. Much like an air tank, if you take a 1 gal tank charged to 120PSI and moved all that air into a 2 gal tank the pressure would drop to 60PSI but the amount of air would be the same.

Similarly, there is probably a restriction in the evaporator if that is where it starts getting cold. The chances of a straight section of tube getting clogged is almost zero, unless its been damaged. However, corners are very likely to accumulate debris.

I'd return that compressor you just got and swap in the evaporator. The dryer is super simple and most likely not the cause, and the compressor is pulling a near perfect vacuum with it can only do if its working properly, just don't operate it like that for long as its not getting the lubrication it needs.

Hopefully you can get it solved without too much hassle.

KenOverton · Jul 19, 2016

dudeman2009 said:
The high side builds pressure only becuase there is a limited volume before it hits the primary restriction, the expansion valve in the liquid line. However, should that restriction be moved down the line, the total volume before the liquid expands is much greater, meaning that more R134 can be compressed without an increase in pressure, since there is more r134 compressed after the compressor, there will be less on the suction side of the compressor.

I would say your compressor is good if it was 95F out, that would indicate that there is low pressure all around. Much like an air tank, if you take a 1 gal tank charged to 120PSI and moved all that air into a 2 gal tank the pressure would drop to 60PSI but the amount of air would be the same.

Similarly, there is probably a restriction in the evaporator if that is where it starts getting cold. The chances of a straight section of tube getting clogged is almost zero, unless its been damaged. However, corners are very likely to accumulate debris.

I'd return that compressor you just got and swap in the evaporator. The dryer is super simple and most likely not the cause, and the compressor is pulling a near perfect vacuum with it can only do if its working properly, just don't operate it like that for long as its not getting the lubrication it needs.

Hopefully you can get it solved without too much hassle.

Makes sense to me. I'll let you know what happens. Neighbor will probably have to pay shipping cost to return compressor.

Thanks for the explanation.

Air conditioner issue

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