Need Help- High Pressure on Discharge Side

[69DropTop]

yeah I thought it was crazy as well and am glad the TXV and sensing bulb were unwrapped or I might have been chasing my tail even longer. I am thinking it's more of the sensing bulb malfunctioning because that is what I was heating up with the rag with hot water on it so hopefully not anything else causing the problem.

My brother is working on an '86 Jag for someone and it needs R12 so I was going to hook my system up to that one to reuse the R12.

I do have a new TXV, condenser, and quick disconnect on hand. I flushed the system out last week and replaced the dryer so hopefully the system is clean and no other junk in it. I was thinking of swapping the TXV, vacuuming and re-charging, anything else you think I need to do?

[bohica2xo]

If things are clean when you open it, then you should be good to go

[69DropTop]

I installed a new TXV this weekend and that appears to have taken care of the problem! Everything appears to be operating normally now, but the output air in the cabin is just a little cooler than ambient so I think I have heat leaking through from the heater core.

[bohica2xo]

Glad to year you are closing in on it. Adjusting the final charge level by monitoring the suction line temperature where the line exits the evaporator case can help you zero in on optimal performance. The inlet & outlet from the evaporator right at the case should be close to the same temperature when things are running right. If you have 36f just past the TXV & 60f on the outlet it is probably still a bit undercharged.

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[69DropTop]

Yeah I'm glad also, put a lot of time and work in it and you helped me quite a bit along the way!

I do want to dial it in to get optimal performance. Factory spec called for 1 3/4 pounds. We put 2 1/3 12oz cans in the system, but I didn't think the evaporator lines were as cold as the should be, I thought at least the inlet to evap would get ice on it, but it didn't. Did I write somewhere I was getting 36*F at evap inlet and 60* at outlet? The evap in/out feel pretty much the same temp to me. We tried using our heat guns on the inlet and outlet, but were getting reading of 120* this was with the engine running so I guess the gun was picking up hot air blowing off the engine?

[bohica2xo]

IR temp "guns" are all but worthless in that application.

36 & 60 were just an example. You can use your hand, the average person can easily feel a 5f difference.

I use a couple of thermocouples under a wrap of presstite tape, but not everybody has that option.

You can also get an idea of how much refrigerant is stacking up in the dryer by adding in small doses & looking for the spike - but this generally requires that you have a way to recover the overcharge.

I would expect a little frost on the line past the TXV.

Easy enough to check for heater interference on a Ford. Pull one heater hose & loop it back to the engine, take all of the hot water out of the core.

[69DropTop]

I wasn't sure what was going on if it was my heat gun or something else. The only other way I have to read temperatures is with the heat sensor adapter that came with my multimeter.

ok, I see now that you were using 36/60 as an example. I felt the in/out of the evap last night and if they aren't the same they are very close to where I can't tell a difference with my hand.

If I were to add more refrigerant what kind of spike would I look for? I doubt I will add anymore at this point since I put in the level the factory spec is, but if we need to add more to that Jag my brother is working on I could add more to my system.

The TXV is just a few inches in front of the firewall, but the little bit of pipe I can see is not getting frosty, but it is sweating and cold to the touch.

Last night I started the car, the engine hadn't been ran for the day so no heat in it. I turned the A/C on and it was colder than the night before because the engine wasn't putting off any heat yet. I was thinking of pinching off one of the heater core feed hoses, but didn't want to pinch the wrong one and risk damaging the core. I am going to order a new water control valve that goes inline to one of the heater lines. I also thought about looping one of the hoses back, but didn't want to mess with spilling coolant, topping off and then doing it again in a few days when the new water control valve comes in.

[bohica2xo]

If you have a stock system on R12 charged with the correct weight, then it comes down to air side issues most of the time.


Heater valves / air doors / seals etc, in the evaporator box & behind the dash. And of course condenser airflow - Fan issues, shrouds seals etc.


Since you are replacing the heater valve that will remove one variable. Spraying water on the condenser can tell you which side of the loop has trouble. With a wet condenser and cool refrigerant int he receiver the evaporator IS getting cold. If the vents are still warm you know where the issue is.


I will take wet & dripping on the exit line from the TXV. Most of the phase change happens inside the box, so the line is mostly liquid that point.

[69DropTop]

Yeah I think it's an air side issue also. Hopefully the water control valve will fix my problem which my little experiment pointed to when I turned the A/C on with the engine cold and then the discharge air got warmer as the engine heated up. I had the TXV and evap outlet lines wrapped in a shirt for insulation, but am going to try and find the right insulation and install it next.

When I charged the system I sprayed the condenser down with water, didn't get much of any pressure change, but didn't monitor output air temp.

I was hoping I would get frosty lines with the R12, but like you said maybe it's frosty cold in the evap box.

[bohica2xo]

The search term for the proper insulation is "Presstite Tape" It is a butyl rubber / ground cork concoction that is self-fusing.

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