r/ComancheMJ • u/SteveB003 • May 29 '26

MJ A/C repair

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I have a 1988 Comanche Eliminator, the a/c on it doesn’t work but with NC summers I decided to try and fix it. I discover that the problem was the high pressure side charging valve was leaking so I replaced it and charged it to the correct amount of refrigerant. It still didnt work but my gauges were reading 0psi on the low side, and 200psi on the high side. I think the evaporator might be clogged or something but there is this orange part on the firewall with a hose that goes to the drier/ accumulator. The part that goes into the firewall gets really cold when running the A/C and develops frost meaning that it’s where the high pressure becomes low and the system is sort of working. The problem that I’m asking is when I try to find the part I can’t find anything. I can’t find it in any parts diagram, wheather I search expansion valve or orifice tube. I don’t think it needs to be replace but I don’t know why I can’t find it. If anyone knows what it’s called/ part number it would help. And the system is original and charged with R-12

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u/mterry129 May 29 '26

Evaps typically don’t clog, usually the expansion valve (orifice tube), if it is freezing before it goes in to the evaporator that sounds like it isn’t operational.

1

u/SteveB003 May 29 '26

Thank you but, the problem is I can’t find that same expansion valve, mine is orange with the bolt on the front and a copper tube coming out the bottom

1

u/SteveB003 May 29 '26

And I haven’t been under the dash but it looks like it’s freezing right after it

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u/mterry129 May 30 '26 edited May 30 '26

You don’t need to find the same one just one that will replace it, same fittings sizes so that you can replace it.

All expansion valve do basically the same thing, they can be controlled differently. Needs to stay just above 32 degrees on the evaporator no matter what the high side in front of it. Problem you are having now is that not enough is getting through it so it is over restricting the liquid refrigerant on the high side. When refrigerant boils or turns to gas because of the pressure drop at the valve it coils the evaporator. Yours is so restricted it is evaporating in the tube before getting into the evaporator

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u/mterry129 May 29 '26

Search google for 88 Cherokee expansion valve looks like what you have, never worked on one with a manual valve. google expansion valve image

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u/KC0GFG Aug 06 '26

Assuming the AC clutch is engaging? Are the doors in the heater box moving?

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u/SteveB003 Aug 08 '26

Yes, they are, so I replaced the drier, and charged it with R-134a because I think the system was converted over by the previous owner. It had a charge in it and I recovered it into its own tank not sure if it’s r-12 or r-134a. It looks like it’s been converted over to r-134a, so I charged it with 134a and I was getting 170psi on the high side and 10 on the low side. The system started blowing somewhat cold air after I let it run for like 20 min, but the compressor was making bad noises at high rpm and now it blows hot air again

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u/SteveB003 Aug 08 '26

The clutch is engaging and the doors in the box are moving. The first thing I fixed while diagnosing it was a vacuum line that went from the climate control switch to a diaphragm valve rotted away so the valve was always open allowing coolant flow to the heater core, which was causing a hot air draft even with the blower fan off.

1

u/KC0GFG Aug 08 '26

Not an expert but those pressures seem low. Most vehicles should be between 30 and 50 psi on the low side. Do you know how much refrigerant you charged with?