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one way check valve? on late 80s Jeeps

Ecomike on Mon April 07, 2008 5:37 PM User is offlineView users profile

Year: 87
Make: Jeep
Model: Wagoneer Ltd (mid size)
Engine Size: 4.0
Refrigerant Type: now 134-a
Ambient Temp: 75
Pressure Low: 25
Pressure High: 180
Country of Origin: United States

I have been doing a 134-a conversion, that as of now includes new hoses, new filter dryer, new expansion valve. It started out as a hose leak R-12 system, late last summer. Got a local shop to replace the hoses with 134-a barrier hoses, custom made. They had problems trying to recharge it, blew the A/C blower fuse so I took over completing the project. Got the wiring and fuse problem fixed. Tried to charge it and got a vacuum on the low side, 28" and 50-100 psi on high side, so I replaced the expansion valve (it was stuck, trashed.... closed, no flow), finally about 3 weeks ago.

Now I am getting about 25-40 psi low side and 50-180 psi high side (high side pressure increased while charging the system) during charging. But it is short cycling during charging, even after adding 2.5 cans and there seems to be very little flow from the high side to the low side, the only difference now is I am not getting a vacuum reading on the low side, but every time the compressor kicks on for 1-2 seconds the low pressure cut out switch shuts the compressor back off. With out an open can of refrigerant feeding the low pressure line it takes about 5 to 10 minutes for the low pressure side to get high enough pressure for the compressor to cycle again.

From a fresh cold morning start it will run for about 6 to 8 seconds before the LP switch cuts out. The compressor seems to run just fine, no noise, builds pressure, etc.

So I am down to a small brass in line part on the filter dryer (now obsolete part at the Jeep dealer, OEM, #J3171794) that seems to be a one way check valve. I have one of them on my 85 jeep also. The inlet and outlet threads are different so bypassing it may be problematic, short of getting a special new HP side hose made again.

What I am wondering is what does this part really do? Why did they install them? Is it really needed? The parts-hose shop I have been working with says they have just scrapped them in the past with no problems, and they have no source for them either. Is there a standard after market part available to replace it?

I am also looking for an R-12 female by R-134a male adapter so that I can attach the new style 134-a yellow hoses to my 20 year old vacuum pumps male R-12 style connector.

chris142 on Mon April 07, 2008 8:43 PM User is offline

It's not a check valve. It's a quick connect. I'm not sure what the story is on them but my assumption is that at the factory they charge the systems before they are put in the car. Once in the car they just screw the quick connect together and send it down the line.

It's not needed and Ihave removed many. They are very common on motorhomes too. I always end up making hoses to replace the ends and using a universal dryer.

mk378 on Mon April 07, 2008 8:54 PM User is offline

Right, you don't need that part, it is just a connection fitting not a valve.

A TXV system should not have a pressure switch on the low side. The switch is on the high side and only detects severe loss of refrigerant, or in some cases it also responds to overpressure as well as under. The switch should never cycle in normal operation. Form those pressures it appears you have normal operation. There is a temperature switch on the evaporator that controls cycling, which should occur rather slowly and only after the vent temperatures come down to close to 40 degrees.

Maybe you have a bad control or other electrical problem if you're sure the pressure is being measured properly and it's not an overpressure issue.

Ecomike on Mon April 07, 2008 8:58 PM User is offlineView users profile

Well it turns out they had already gutted the QC/check valve, so it was not the problem after all. It was already hollowed out (the spring piston assembly had been back threaded out of the housing and tossed, and just the empty housing reinstalled), so now I am wondering what the real problem is?

Still not getting refrigerant flow from the high pressure side to the low pressure side.

Bad new expansion valve, plugged filter drier, or ?????

Any ideas???

The expansion valve and dryer are essentially new and unused. Should I try charging it again and just tap the new expansion valve with a hammer?

Ecomike on Mon April 07, 2008 9:12 PM User is offlineView users profile

Thanks for the feedback guys!


Are you saying it is normal for the pressure on the low side to drop to 25 psig, and high side to go to 180 psig in 2 seconds of run time, and for the compressor to cut off for 10 minutes afterwards, and for it to then take 10 minutes for the low pressure to reach 40 psig before the compressor kicks on again? Oh and it does not get cold.

It is consistently cutting off at 25 psig on the low side, and back on at 40 psig on the low side. High side pressure on my gauge has been independent of the cut on and cut off pressure. I could force it to cut on regularly during the fill process by warming the refrigerant bottle in my hands to force more refrigerant into the low pressure side, faster, it always cut back on at 40 psig during the filling process. Once I stopped filling it, it sat there at 25/180 psig for ten minutes before the low side finally got to 40 psig and it repeated the cycle.

Ecomike on Mon April 07, 2008 9:17 PM User is offlineView users profile

My Haynes manual's Electric drawing shows a low pressure switch and a thermostat switch in the lines for 86-90 models. It does not show a high pressure switch in those years, which I believe was added in later years. The old ones like mine just had a high pressure relief dump valve IIRC.

mk378 on Mon April 07, 2008 9:25 PM User is offline

It is normal for the pressures to go to 180 and 25, under those conditions the compressor should stay running and it should get cold inside.

Something is making it stop abnormally early. Use a voltmeter to see which switch is opening up. I think if you look at the lines carefully you will find the low pressure switch is actually measuring high side pressure.

You may be a bit overcharged for the high to go up so high, or maybe there is a fan issue (any electric fans if equipped should come on whenever the compressor is on). But that won't be a problem yet if the ambient is only 75 degrees.

mk378 on Mon April 07, 2008 9:29 PM User is offline

It's also possible you are not measuring the high side pressure properly and there is a high pressure switch cutting it off. The high side should drop somewhat, shortly after the compressor stops. If you have isolation/service valves right at the compressor make sure they are both slightly off of full open, that is the pressure measurign position.

Ecomike on Tue April 08, 2008 11:56 AM User is offlineView users profile

Yes, there is a switch on the high pressure side mounted on the filter dryer assy.

The electric fan is cycling on and off with the compressor clutch, it is working properly.

It (the cycling) reacted the same way all the way from the first oz of refrigerant, to the last oz I added. I never got past about a 3/5ths fill, so there is no way it got anywhere near overcharged. I stopped charging it when the high side hit 180 psi and when I still had no evidence of proper refrigerant flow through the expansion valve.

I removed the old service valves and replaced them with non-valve, open flow fittings that are native to R-134a quick connects and native to the compressor blocks external fittings (about 1" dia male fittings, sorry I don't the designation on that fitting), so that area is wide open. I am measuring the inlet and outlet pressures right at, or just outside of the compressor itself, so I am reading exactly what the compressor is seeing. But, I am not necessarily measuring what a downline pressure sensor may be seeing at or after the filter dryer.

Just for clarity, both gauges read the same pressure at start up, and the high side pressure took nearly an hour to get up to 180 psig during the agonizingly slow fill process. Had no more than 26 oz R-134a in the system when I stopped.

Something has got to be holding the flow back between the compressor high side outlet and the expansion valve. How likely is a bad expansion valve off the shelf?

Ecomike on Tue April 08, 2008 12:43 PM User is offlineView users profile

Well I am getting closer to figuring it out. I thought I had pulled all the refrigerant out last night to get access to that QC/valve fitting, just discovered there was more refrigerant trapped between the compressor outlet and the filter dryer, so the filter dryer must be plugged. The service guy says they cleaned a lot of c*ap of of the condenser before installing the new hoses and new filter dryer late last year. All I can figure is some more stuff came loose and plugged the filter dryer. I am picking up a new dryer now.

They are telling me the switch that comes with and mounted on the dryer is a trinary switch, that cuts off at high and low pressure in the same switch! ????

mk378 on Tue April 08, 2008 1:29 PM User is offline

If you have debris in the system it needs to be fully flushed. Replace the condenser, it is the hardest part to flush and yours is not coming clean. Debris will clog up expansion valves quickly, it is the part with the smallest opening.

Pressures still don't make a lot of sense. If you have a near total restriction anywhere, the low side at the compressor should go below zero. Unless the compressor isn't working very well either.

Ecomike on Sun April 13, 2008 2:25 PM User is offlineView users profile

So what is the point of the filter/dryer between the condenser and the expansion valve? LOL!

Ecomike on Tue April 22, 2008 12:12 PM User is offlineView users profile

Turned out the condenser is somehow plugged. The AC shop I entrusted the hose replacement to in Sept last year soldered (or brazed) new fitting adapters onto the original condenser to help with the hose upgrade (R-12 to R-134a), so I am hoping they screwed up the solder job on the new fittings on the end of the old condenser. If not I guess I will be buying a new condenser. I just don't have good luck when I let other people work on my vehicles. These guys have been around for nearly 50 years doing AC retrofits and wholesaling auto AC stuff so its not like they don't know what they are doing, just my bad luck. The condenser was working fine before they installed the fittings.

Ecomike on Mon May 12, 2008 1:01 AM User is offlineView users profile

Well I was right, the condenser is still good, the AC shop tech that brazed / welded the aluminum tube adapters / extensions onto the old aluminum tubes they salvaged off the old OEM hoses, one of them was botched, they managed to filled the aluminum solder joint ID up with solder / aluminum. What a waist of time, they should have flow tested their work before they installed it, end of story. That is what happens when busy mechanics get interrupted and forget where they were on a job.

It blows VERRRY cold air now, I am impressed, seems even colder than R12 ever got in it, as best as I can recall. Nice pressures, seems to be good to go now.

Thanks for help guys!

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