Air Conditioner Questions, Hoses, Manifolds, Valves

[dirtymac]

We are slowly working our way through the A/C rebuild.  We are close to getting everything back together.  We have the evaporator and condenser installed.  We have a compressor coming this week (the last one did not fit).  We have a new dryer, orifice tube, o-rings, electrical pigtails, etc.

Our hoses are not in great shape and one has a nasty looking hole in it.  Another partially broke off in the old condenser.  So we are working on new hoses.  We have a place locally that we think can make them for us so we are going that route.  The current issues are all related to the hoses.

We have our old hoses so we know the shapes, sizes, types, and such to make new ones.

We found a junkyard truck just like ours with nearly everything in it intact.  The A/C was all there but in worse shape than ours.  But we notice that truck had what the service manual refers to as "manual valves."  The documents on the forum suggest they are for isolating the compressor from the system.  Presumably to replace it without emptying the entire system.  I have not read beyond that yet.

Our compressor does not have these.  Clearly they are not required but are they helpful?  If they are something you'd suggest we get, can you point us to any?

The next issue is that our manifolds are not in the best shape.  They seem functioning but they are heavily scarred and beat-up.  This is mostly cosmetic but they have sharp spots on them.  Can anyone suggest what type of sand paper or file I could use to clean them up with?  The mounting surface is a little dirty but I'm not sure what would be safe to clean it with.

Finally, one of our manifolds has a little tube coming off of it.  I cannot figure out what this thing is.it is coming off the left side of the manifold on the right.

[grumpin]

 A way to manually isolate the compressor is neat, but I don't think I've ever had a failure where a leak didn't cause the compressor failure. So up to you on those manual valves.

I would probably clean the manifolds with a wire brush.

The tube on the manifold is a pressure relief valve.

[mat in tn]

that will be a fuse. an overpressure relief. this is a means of controlling the breach so to speak. as opposed to having a different part fail under high pressure and causing potentially more harm. cleaning up those manifolds is just a preference. 220 wet/ dry sandpaper should do fine. they are aluminum and should cut easily.
 as to the units with king valves, they are helpful in isolating the rest of the system. one, from refrigerant loss and two, from allowing moisture or dirt into the system. however, the proper way is to evacuate the system fully before opening it. tape over any openings unless you have proper rubber plugs at hand. when getting ready to seal up the system that last time prior to charging you will need to evacuate again. this time to remove moisture (non-condensable). air and moisture behave very different than refrigerant in a sealed environment. this is what the drier is for, but it has a very limited capacity. in fact, I have done a full evacuation with the old drier in place and let the vacuum run an extended time before swapping to the new one and vacuum again. many say unneeded but what does it hurt. exercise patience on the vacuum hold test. if the system cannot maintain the achieved vacuum, then it cannot hold pressure either.

[dirtymac]

We finally got back to this today.  It took some time to get all of the parts together and the time to work on things.  Everything went well until we noticed the pressure relief valve dripping bright yellow liquid.

A few key points:

1) We pulled vacuum for 5 minutes and then let it sit for an hour.  No leaks.  We then pulled vacuum for 45 minutes and no leaks.  Gauges looked good.
2) The compressor (4 Seasons) came with 3oz of oil and the paperwork said not to remove it.  The service manual stated the system needed 10oz of oil, so we added another 5oz to the compressor according to 4 Seasons instructions and added another 2oz to the evaporator.
3) The A/C sticker stated 56oz max for R-12.  We used 80% of that for the R-134a.
4) Compressor engaged and the air blew cold for a good 20 minutes before we noticed the leak and not soon after that the compressor started to rapidly disengage/re-engage.
5) The relief valve only leaks when the compressor is engaged.  If you turn off the A/C the leak stops almost immediately.

My bet guess is that the pressure relief valve (being 42 years old) is shot.  I'm also guessing we have now lost enough Freon to cause the compressor to not engage correctly.

I found a part at Rock Auto, Motorcraft TF49, which looks pretty similar.  Has anyone used it and, if we do replace it, I'm guessing we will need to remove whatever Freon is left in the system.

[viven44]

Can you share a pic of that sticker that says 56oz max ? That is an awful lot of refrigerant to be used in a bullnose truck.....

Update: I did see the factory manual. It does show 3.5 lbs... wow!! Even a modern Suburban with the spacious cabin takes only 2.2lbs.

What are your high and low side operating pressures anyway ? Just want to make sure the system isn't overcharged....

[Rockhauler]

Vivek

Here's a couple stickers from my trucks. One is the original that Ford installed for R-12 the other is from a shop that changed my truck to R-135a refrigerant.

These were taken from my 1985 F250 6.9 diesel truck, and my 1986 F150 4.9 has the same amount for the Ford sticker.

[viven44]

Thanks for that Paul.... The 81 factory manual documentation here under HVAC mentions that as well... just surprised is all.

[dirtymac]

We are running some tests this morning to get some more accurate readings and I'll get back with you on those.  This morning she isn't leaking but it's also still 10 degrees cooler than it was last night.  That's changing rapidly though :)

[dirtymac]

When we got started this morning the ambient temperature outside was around 88.  The static pressures from the Low and High side were just above 100psi.  From the charts I have found this appears to be accurate.

We ran everything for about 20 minutes.  No leaks.  Low pressure hung around 50psi and High pressure around 330psi.  Using 90 degrees for the ambient temperature, the Low pressure was good and the High pressure was High.  After cutting the A/C off it equalized to about 105psi.  After that we let everything sit for about an hour.

By this point the outside temperature was 95.  The static pressure was still about 110psi.  Everything ran for about 10 minutes and then the pressure relief valve started to drip (slower than last night).  Low side pressure was 55psi and High side pressure was 350psi.

Now came the fun part.  We turned off the A/C and let the static pressure equalize.  The plan was to unplug the gauges, reset evertyhing, and test again from scratch.  I'm not sure what happened in the frenzy that ensued but when we removed the Low side connector the schrader valve stuck open.  It took us several minutes to get the thing straightened back out and stop the leak.  We definitely lost some Freon.

Started everything back up.  Pressure valve is still leaking at this point.  Low side pressure has now dropped to about 40 psi and High side has dropped to 295psi.  This would seem consistent with the loss of Freon but the pressure valve is still dripping until we turn the A/C off.

We are wondering about all of the talk of Ambient temperatures.  Sure, it's 96 outside at this point, but under the hood its probably 110 or higher.  Is that affect the pressure release valve?  Could it just be bad?  I haven't been able to locate any specifics on the valve other than what it does.

[viven44]

Where is this pressure valve located? Got a picture of it ? I wasn't aware of a pressure relief valve in the bullnose AC system...

[dirtymac]

It's built into the discharge side of the compressor manifold.  The picture in my original post on this thread has it.  I can get you one of it on the truck.

The weird thing is that it just drips.  I haven't found a lot online about these but the few videos I found show them blowing air, not dripping.

[viven44]

I found it!! Didn’t know that was a pressure relief valve. I always wondered why this system was allowed to function without any high side pressure switch…

I am seeing some old ooze but nothing significant.

[viven44]

Your pressures were definitely high and I’m glad you had that leak

It’s very strange that pressure relief valve is still leaking though. May be time to replace it.

I think the one you found on Rockauto seems to be the correct one

https://www.rockauto.com/en/moreinfo.php?pk=3102783&cc=0&pt=6696&jsn=318

PS: I just read above and noticed the comments from others identifying it as the pressure relief valve

[mat in tn]

there is another point to bring up. all of these temp pressure variances are also dependent on available air flow. the pressures will be higher if the thermostatic fan clutch is failing to engage enough. are you able to hear the fan engage and "load up" as temps rise? on a properly operating one you can often hear the air flow cycle in a range of stronger, weaker, stronger, weaker continuously at operating temp with ac on the rate will vary up to the point of continuous at higher temps. and yes it will be different with the hood closed and or driving.

[85lebaront2]

These systems pre-date the high pressure switch. The relief valve is the safety on them. High pressure switches came into use when the government regulations required full containment for refrigerant.

One of the steps in doing an R134a retrofit was to remove the relief valve and replace it with a high pressure switch.

I only had one vehicle that I couldn't convert, a 1985 Chrysler Lebaron convertible. The condenser design and mounting did not get adequate air flow when sitting still which resulted in tripping the high pressure switch, or burning up the compressor drive belt.

[viven44]

Thanks.. great info Bill,

I need to source a high side pressure switch for future use...

[dirtymac]

In fact, we have been discussing this as a possible issue for the last several weeks.  We have been dealing with some high coolant temps the last few weeks.  I suspected most of the problem was our radiator, which has developed a small hole above the intake hose.  It doesn't leak (that we have seen) but it does steam.  Water usage has been minimal.  While working on the A/C, we discovered that even full, with good water flow, the engine coolant was still getting hotter than normal while parked.

We ordered a new radiator last night.  We had been putting this off until after the A/C was done because we have a heater core bypass valve to install, and a new thermostat.

This morning we were discussing the fan clutch again and decided to go ahead and replace it.  We are not hearing the click some people mention or the fan loading up.  It generally seems to turn the same, winter, summer, fall, etc.  We have a severe duty clutch on order.

If all goes to plan, we will have all of that and the pressure relief valve installed this weekend.

[dirtymac]

Do you know of a high pressure relief valve for the factory manifolds?

[mat in tn]

if you are thinking of an extra high pressure then no. I would not do that anyway. that would be a similar thing to putting a 30 amp fuse in a 10 amp circuit.
I have not heard any "click" before from a fan clutch but have always listened for the load change from the air flow. get as good of a radiator as you can. I use factory replacements mostly but will go as large of capacity as is available. many go with fabricated aluminum, and I like them too, but I still prefer the factory look for most of my vehicles.

[viven44]

What does the 'click' mean ? For anything I have recharged myself, I usually go by the chart on the factory manual (ambient temp, low side, high side).... the ambient temp chart is important because when the recharge is done the hood is open so the ambient is the dominant factor.....

I have come across trucks that had a 'click'... so I was wondering what that meant..