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Extreme hi pressure

donandmax on Fri September 19, 2008 12:13 PM User is offline

Year: 1980
Make: Dodge
Model: Motorhome
Engine Size: 360
Refrigerant Type: R=134 (retro)
Pressure High: 450 psi
Country of Origin: United States

This is an aftermarket system. That was ruined by adding 134 refrigerant with stop leak in it. service man added the following: new, york compressor, expansion valve, receiver dryer, condenser and fittings. Usual prep. Unit has a clicking noise (same as old compressor) and hi pressures (450PSI) He has replaced everything new and we still get this "clicking" noice from the compressor and high pressures. Temp today was only about 60 deg. when he tried it out and even though the high side was only 150 psi still had this clicking sound coming from compressor. As the day warms up pressures are again headed for the high side. He is in touch with very knowledgeable technicians and they say to return the compressor for another one. I say if the old and new one gave same problem something else must be wrong. But I agree with him this whole thing doesnt make sense. A whole new system and still these high pressure problems. He's evacuated and vacuumed etc. all the things that should be done.Is it possible that the York compressor won,t handle R134 but likes the R 12 better ? I'll owe him 1500.00 in repairs but him and others are stumped. He's been workin on auto air for 25 yrs and says he has never had anything like this. This thing is "eating his lunch" because he has had a bunch of hours on it that he says can't be recovered.(otherwise I would owe him several thousands dollars !
Anybody got any ideas of whats happening here ?

TRB on Fri September 19, 2008 12:44 PM User is offlineView users profile

You may have damaged the compressor at those pressures. What type of condenser was used when replaced? Hoses can also be clogged or restricted from sealer!


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GM Tech on Fri September 19, 2008 7:07 PM User is offline

Are you being fooled by isolation valves at the top of that York compressor?-- My first experience I had with them I blew out the head gasket on the compressor- because the valve was clear open which is in the isolation position where the compressor communicates with gage set only- the rest of the system is shut off (isolated) from the compressor-here is what they look like-- They are used a lot on big systems- like a motor home or tractor.

The trick is to not open them all the way, only half way to run and measure pressures....

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Fri September 19, 2008 at 7:08 PM by GM Tech

donandmax on Sat September 20, 2008 11:05 AM User is offline

The a/c repairman says there are no such valves on this compressor. He was surprised there wer'nt any. This extremely high pressure showed up immediately after installing new system. Everything was changed except the evaporator under the dash.

rockfoot on Sat September 20, 2008 12:11 PM User is offline

If the evaporator is clogged it would cause a high pressure... There is a probe/switch on there somewhere that is supposed to feel the superheat back to the compressor after it leaves the evaporator. This probe/switch should cut out the clutch before those pressures are reached.... that is, if the evaporator is clear and the fan on the evap is working... You probably knew this already.. is the return side getting cold?? my 2cents worth...

Edited: Sat September 20, 2008 at 12:12 PM by rockfoot

iceman2555 on Sat September 20, 2008 7:15 PM User is offlineView users profile

Typically if stop leak is a part of the refrigerant is quite possible that this chemical is not the type that will 'harden' within the system. This type of stop leak is typically a 'conditioner' type stop leak.
That being said....still best not to use this stuff.
Where are the service ports located on this system...are they located on the compressor similar to the photo supplied by GMtech...or at other points in the system. Also there were no low side pressure post...these can be helpful also.
If the ports are on the compressor..or in the line between the compressor and condenser...this is the discharge side of the system. An excessive high side at this point typically is indicative of a restriction within the condenser...or possibly a drier that is installed with a reverse flow patter....the drier is installed backward.
If the service port is after the condenser/drier...the problem could still be a restriction...but first place to look would be a possible engine cooling problem. Especially since the post states that as the day gets warmer the pressures began to increase.
But first a look backward....the first and most important aspect is to know that the system is properly recharged. Too much refrigerant will, of course, offer some serious pressure issues.
To determine a possible restriction...obtain a temperature measurement device....Sears sells a voltage/amp meter with a temp probe for less than $60.00....these are pretty good little units.
A test procedure is to check between each connection....hose to hose....inlet and outlet of the determine if a restriction exist. Check the inlet/outlet temps of the not simply believe the 'flow could be attached incorrectly. Of course, if the drier has different size inlet/outlet fittings this negates the installation problem..but the drier should still be checked.
The cooling system must be 'up to par' to work on a coach and use 134a....a slipping fan clutch....a restricted radiator....a missing fan shroud....all these items should be check.
Does the unit have an aux tranny cooler mounted on the so..this may need to be relocated....this excessive heat could result in a possible pressure problem.
One of the 'older' test...simply spray water on the condenser during this 'high pressure' moment...if the pressures drop...significantly....look for a cooling system problem.
Are these an elevated engine RPM or at idle. Makes a difference...esp when a retro has been accomplished.
Does this vehicle cool? Not quite sure what 'rockfoot' was trying to express....but is the lines are cool...(low side) and warm to hot (high side) the system should be cooling. A high side pressure of this magnitude would produce a line temp that would be almost impossible to touch. Check these temps with the above mentioned tool. Temperatures are more indicative of a potential system problem than pressures...since pressures are determined at only two locations.
Make some results....lets see what comes up.
But first and foremost...make sure the system is properly recharged. the condenser constructed of aluminum...or brass and copper. Is it a tube and fin....or a more efficient parallel flow or 6mm pic?
Give us a bit more info....this problem can be solved....
Also one other aspect...esp for the noise issue...what type compressor is being used on this vehicle. Just curious.

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NickD on Sun September 21, 2008 9:21 AM User is offline

The a/c repairman says there are no such valves on this compressor. He was surprised there wer'nt any. This extremely high pressure showed up immediately after installing new system. Everything was changed except the evaporator under the dash.

The valves are more part of the vehicle than the compressor, he had to jury rig to get around them, since I have a system similar to yours, mine uses a receiver with an expansion valve, has the valves, and an evaporator thermal switch that cycles the compressor. I really do not know what you have unless you want to supply a bunch of pictures. York compressors are noisy, added sound damping insulation to my doghouse since it's only inches from me that has helped. Do you have an expansion valve? Was it replaced? Assume that clicking is the compressor clutch cycling.

Does your guy know AC theory? That helps to make sure your system is even operable.

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