Automotive Air Conditioning Information Forum

It's been a long while since I've been on here. I'm trying to revive an AC on a new to me 1984 Isuzu PUP that hasn't had the AC working for several years. It still has some pressure on it but not much Freon in it, just enough to be positive of about 40 pounds. I pulled a vacuum on it and it held well so I charged it up with 30 oz. measured of my R12 that I had been saving. As soon as it was turned on the low side went into a -25 vacuum and the high stayed at about 100 pounds. I figured that it was the expansion valve stuck. I've had this same issue on other PUP's that I've worked on. I recovered most of the R-12 for later use. I replace the valve with a 4 Season. I lost a little oil while working with the evaporator out so I added 2 oz. of oil, thinking that after 32 years that it has lost some oil also. I checked the Thermostatic Switch while it out in a glass of ice with a lot of salt and it was clicking on and off. I did not flush the system. As I was putting the lines back on the evaporator I noticed that the opening of the high pressure joint was about half closed. These are flare joints. After checking both sides of the lines. It was some substance that was hard and a dark tan in color. I had to use different size drill bit to clean both lines to their normal ID. Was this from a sealer some one may have added to the system? Knowing the guy that owned it since new, I wouldn't put it passed him.

Outside temp is 96 degrees today. After cleaning and reassembling, I pulled a vacuum down to 400 microns and that held at 550- microns for about 20 hours. So I added 1 more oz. of oil. System requires 5oz. And loaded 30 oz. of R-12 into the vacuum before cracking up. The pressure at idle are 50 on the low and 250 on the high. This with a big fan on the evaporator to cool. There aren't any shields around the fan on these PUP's, they were add on systems at the dealers back then, even though they are the AC that came from Isuzu. If I remove the fan the high side can go up to almost 400 pounds while the low stays about 50 pounds. If I run the system at about 2,000 RPM, and with the extra outside fan on the front, the high side comes down to about 250 and the low stays about 45 to 50 pounds. But the compressor will cycle right frequency by the Thermostatic switch like it was trying to freeze up. I have not tried it on the road yet.

How much temp drop should the condenser have across it. I have about 15 degrees. Spraying water on the condenser really drops the high and low side really quick so it act's like not enough air across the condenser. I thought it should be in the 20 to 25 degrees range. If someone added stop leak, I'm wondering if the condenser and drier are stopped up. I see a few bubbles in the sight glass but I did put the requires 30 oz. in. Major parts aren't easy to come by for these old PUP's. Any suggestions on getting the pressures down.

GeraldK4NHN
Cayce, SC
"One test is worth a 1,000 opinions"

This will be challenging, for sure.

GeraldK4nhn wrote:This with a big fan on the evaporator to cool.

I think you meant condenser.

Thanks for catching that.

Yes I did mean condenser, my proof reading didn't catch that. These ole eyes aren't what they use to be. 80+ years


GeraldK4NHN
Cayce, SC
"One test is worth a 1,000 opinions"

Something else that I posted wrong was the pressures, shouldn't be in pounds, but stated as PSI. Again these ole eyes and mind aren't together.


GeraldK4NHN
Cayce, SC
"One test is worth a 1,000 opinions"

The brown solids sound like sealer.

Did you find any of that in the TXV?

I'll look tomorrow at the ole one real close. It didn't just jump out at me when I removed it. This is the third TXV that I've had stuck in about 6 that I have worked on over the past 4-5 years. Most of the PUP's AC haven't worked for years when I get to work on them. The evaporator unit isn't much trouble to remove, Remove the glove box, 3 retaining 10mm nut, break loose the 2 AC lines and out it comes. Usually the biggest problem is getting the Low side connection loose. Alum male and steel female can be a bitch to get apart sometimes.

If you have a system full of sealer, you will be replacing parts.

The evaporator looks like it is still available.

Even if the condenser is available, I think I would swap to a Parallel Flow unit - because the hoses are full of sealer & need to be replaced anyway.

Basically a system replacement, but it will cool nicely when done. Tim lists this one:

http://www.ackits.com/cn-20009xc-econom ... 0condenser

Should be close to the core width of the Isuzu radiator.

I looked real close into the ports of the expansion valve and I only saw a little dirty oil. Wiping it out with a q-tip, I didn't feel any solids in it. I've always want a parallel flow for my 83 PUP, which is the same as my son's 84, but plumbing it up I'm not sure is feasible. The unit posted has both in and outlet are on the same side. The one that is in there now, is factory, and isn't much room to even work with the lines now. I may reclaim what's in there now and try and do a flush and replace the drier. I thought that I had a fan shroud to put on it but it was from an earlier model and would quite fit around the lower water hose. I know that would give me better air flow making the air all come thru the condenser and radiator and not just from under the hood. Does anyone know how much temperature drop there should be on the condenser. With force air flow, outside fan, the pressures start falling in line and with a small water spray, it really falls in line.

GeraldK4nhn wrote: I thought that I had a fan shroud to put on it but it was from an earlier model and would quite fit around the lower water hose. I know that would give me better air flow making the air all come thru the condenser and radiator and not just from under the hood. Does anyone know how much temperature drop there should be on the condenser. With force air flow, outside fan, the pressures start falling in line and with a small water spray, it really falls in line.

Fan shroud is important, got to get that condenser cool enough where the hot gaseous refrigerant condenses to a hot liquid; lowering the temperature of such hot liquid is pretty insignificant. Also check your fan clutch, but you really need the fan shroud.

Thanks for all of the replies. I've done a lot of reading today trying to find the answer to one of my question about the cooling temperature of the condenser. I ran across this and it pretty much say what your comment is. That shroud is going to be real important. I have my feelers out to the Isuzu group for a shroud. Finding parts for a 30+ year old PUP isn't easy.

Going back to my first post had me thinking about this. I have 15 degrees cooling and I was thinking it should in the 20 to 25 degrees and I found this and I think it confirms yours and my thoughts. Not enough air going across the condenser.

Minor or major restriction, faulty cooling fans or fan clutch, or poor airflow across the condenser prevent refrigerant from cooling down properly. The resulting warmer air or extensive back-pressure often causes damage to the compressor. To detect this problem, users may check the temperature of the condenser's inlet and outlet with the A/C on the highest setting and all windows and doors open. A 20-40 degree temperature difference between the inlet and outlet is normal.

Less than 20 degrees indicates and airflow problem and greater than 40 indicates a restriction problem. Each problem is preventable with regular flushing and cleaning of the A/C system. If too much damage exists, the user must replace the entire condenser

You guys have a lot more experience doing this work than I have and I respect all of you guys input.

Now to locate a shroud.