Need Help- High Pressure on Discharge Side

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69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Wed Aug 15, 2018 1:03 pm

So, I put a whole 12oz can in it, got the pressures up a bit, but the low side kept dropping back to 12ish psi after the system had been on for a while and shutting off the compressor. I went ahead and ordered all new lines for it, with a sight glass. At sometime it looks like someone bent the hardline coming out of the evap core and bent it back up, it still has a slight kink in it and I didn't want to try to bend it back anymore and risk damaging the hardline. Could this cause the problem we are seeing with the low side pressures or do you think I just have a leak somewhere, such as the factory suction hose I mentioned earlier?
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Wed Aug 15, 2018 3:50 pm

At this point the factory suction hose is already suspect because of the weeping dye. It could have a partially collapsed liner. If this was a POA system I would suspect the POA valve.

I don't remember much about that model year. Only that 69/70 was a 2 year run before they changed things again. As I recall the OEM evaporator was a tube & fin assembly with copper tubes. If you have a kink in a tube it can be repaired, but proceed with caution. It would be best to isolate the kinked area with wet rags & anneal the copper where the kink is first. 49 year old copper has age hardened some and is work hardened where the kink is.

I did notice that the dealer installed A/C TXV is most common. I don't know if the OEM valve has a higher CV.

The fact that you added 12 ounces with no change to the suction side points to the TXV / Evaporator / Suction hose part of the loop.

What was the high side pressure rise with the additional 12 ounces?
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Thu Aug 16, 2018 8:21 am

I meant to take another look at the suction hose last night in the dark with the UV light but forgot.

This is what the evaporator core looks like in my '69: https://secure.cougarpartscatalog.com/s ... attribs=87

The evaporator repair procedure you described is out of the range of what I am able to do at home and I would probably either need to take it to a professional to get repaired or buy a good used one like in the link above. Do you think it's possible for a pro to do that repair on the car or would I need to pull the hvac box and remove the evaporator?

I just replaced the TXV a couple weeks ago and that solved my high side high pressure issue I was having. Hmm, what would you suggest I do from here, go ahead and replace the suction hose and see what happens?

The highest I saw the high side after adding the 12oz can was 225 at idle. I forgot to write down the high side pressure off-idle, but can do that tonight if you need me to and report back. It might be worth mentioning that after adding the 12oz can the low side would hang around 20 for a while then "walk" down to 12psi and then the compressor would shut off

Thanks for all of the replies and info so far! :)
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Thu Aug 16, 2018 9:01 am

You would have to remove the evaporator from the car to anneal the tube.

Have you ever had the evaporator out of the car? What sort of shape is it in overall?

If the suction hose is OEM & weeping dye, I would replace it. Sounds like you are at a spot where recovering things & replacing a hose while working on the evaporator are the best path.

Without seeing the "kink" I can only guess what effect it may have. But there may be other issues at the evaporator. The fact that adding 12 ounces of refrigerant brought things up, but eventually it all stacked up in the high side could be a blockage at the evaporator, or simply a freezing evaporator with the air rushing around it without cooling.

With the cabin fan disconnected your system should do exactly that - the TXV goes to minimum, the refrigerant liquid gets stored on the high side & eventually the low temp switch stops the compressor.
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Thu Aug 16, 2018 10:11 am

Ok, I kind of figured the evap would have to be pulled to do the repair :cry: I have not had the evaportor core out of the car yet, but was thinking of pulling the dash and hvac box out this winter, just not something I feel like doing now or have time for. My goal was to have working A/C this summer, but I've been thrown a couple curve balls and if it doesn't work out I will survive.

The suction hose appears to be OEM if not it is definitely very old. The green was a darker green and it was only on the front half of the hose nearest the compressor so not sure if maybe it's older dye or if something else got on it to do that. I thought I saw some brighter newer looking dye on some of it, but want to verify that. I don't mind replacing all of the hoses. My original plan was to get the A/C going this year and if it leaked the charge out over the winter replace all of the hoses next spring.

The kink is on the bottom so not sure if i can get a picture of it or not to show you. It's not horrible, but I could see how it could restrict some flow. I'm thinking it is more of the evaporator freezing up or the evaporator being dirty and air not flowing across it. When I had the system open a couple weeks ago I blew air through the evap core, not sure if this says it's not plugged up, but I barely opened the blow gun nozzle and air would come out of the other side. I would think if there is a restriction it would be harder to blow air through it, but I'm not sure about that.
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Thu Aug 16, 2018 1:06 pm

Well, yeah if you have not had the box out to rebuild it, then your refrigeration system is probably working very well.

The kink could be more than 20 years old, and may have been straightened enough right when it happened. Sleeping dogs & all of that - for now.

The likelihood of the foam seals being gone to crumbs, and possibly blocking the airside are very good. Unless you have owned the car from new, you will likely find tree leaves & needles from trees you have never seen before.

The box is not as bad as some for removal. Probably a video of it online - the Mustang is a popular car. If that was not a 2 year only car, there would be brand new (repop) evaporators available.
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Thu Aug 16, 2018 1:24 pm

Yeah, I have no clue how long the kink has been there and what not. Before I installed the prestite tape neither of the evap tubes were freezing so not sure if that is enough to tell us if the the core was freezing up or not. On humid days there is a steady drip of water coming out of the box, but once again not sure if that is enough to tell us if it's freezing up or not.

I had the same thought that all of the foam seals in the box have probably turned to dust by now.

The guy that owns the company I linked the evap core to has a great video of how to get the box out and rebuild it, just something I didn't have on my list of things to do this summer. Do you think that it is more of an issue with the evap core and it's not low on charge? They do make repro evaporators, but apparently are aluminum and more susceptible to corrosion than the factory stuff.
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Thu Aug 16, 2018 2:34 pm

Nothing rots an evaporator better than 2 cups of pine needles & oak leaves in the case, kept wet with condensation. It looks like the used evaporator you linked to had about a cup in there with it, based on the corrosion on one end.

An aluminum evaporator would be just fine unless you park under trees year round. What sort of construction are the aluminum units?

.
69DropTop
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Re: Need Help- High Pressure on Discharge Side

Postby 69DropTop » Thu Aug 16, 2018 3:10 pm

I'm not sure what the construction of the aluminum core is, but here is a link to it: https://secure.cougarpartscatalog.com/1 ... attribs=87
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bohica2xo
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Re: Need Help- High Pressure on Discharge Side

Postby bohica2xo » Thu Aug 16, 2018 3:30 pm

That unit is the same as OEM - Copper Tubes with Aluminum fins. A nice copy actually.

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