Newbie Looking for advice

[Jaz]

I am just starting to learn about ac systems, I have worked on them for a few years removing old R12 systems and fitting all new components with the exception of the evaporator on classic cars.It also helps I am a qualified auto electrician so the wiring side is no problem.
However due to problems getting decent ac engineers to properly nitrogen pressure test systems and vac them for more than 5-10 minutes before filling them for me I am now learning the gas side and working with the gauges.

Ive just got some gauges and a vac pump and hooked up to my own car that was converted to R134a 8 years ago and had the gas topped up 3 years ago.
Looking at the sightglass it seems to have many bubbles and needs more gas but when I hooked up the gauges I got the following readings


Ambient 20c 68f
Low pressure 45-50psi
High pressure 180-250psi
Temp at vent 16c 61f
Fans cut in at 245 and out at 180psi
Heavy stream of bubbles in sight glass

I am a novice but the pressures looked ok to me so does it really need more gas and if so how much, I know the weight from empty but how do you know what to add to a partially charged system.

The car is a Jensen Interceptor 1972 and for those not familiar with this car they have a Chrysler 383 engine with a Chrysler ac system and it is running a modern York style compressor.

[tbirdtbird]

OK, so you want to learn.
Suggest you go back a ways on this forum and read every thread and post and you will learn a lot.

Some pointers:
1. the sight glass is to be ignored for R134, it is relevant only to R12
2. You are correct, 15 min is too short a time to pull a vac. Should be more like 30 min, but for novices I usually suggest 1 hr.
Hopefully you have good equipment, such as an electric motor type vac pump (not the compressed air type)
3. Be wary of youtube vids, many are inaccurate
4. 68° is honestly too low to be checking a system, very little work is being done by the comp. No doubt it will behave differently at 80, which is the range we like to test and charge our systems, UNLESS you have a modern car where the amount of refrigerant is specified on the under hood label, in which case you can properly weigh in the charge. But I would not test it at such a low ambient
5. We (and you) would want all pressures to be at 1500 RPM. Anything less does not help test the system
6. You give a range of pressures and I don't get that, you should get a steady pressure reading at a given RPM. Always test with temp setting at coldest and fan on max, with windows open
7. I am not sure why any mfg would cycle the fans the way yours do. We like the condenser fans on at all times if the comp is running, your pressures and cooling will be better
8. If you know the correct charge by weight, and you feel the charge is off, then have the charge reclaimed and re-charge fresh by weight, then you will know if the system is working correctly or not

[bohica2xo]

Jensen Interceptor's are quirky.

Given the pressures and temps you are listing at 68f ambient I would suspect reheating or there is an obstruction someplace. Likely some of each.

With the fans on I would expect a high side around 180 psi. Which you have. You have liquid in the sight glass - some bubbles are always there with 134a. If it looked like shaving cream I would want to see it recovered and a full charge put back in.

The low side at 50 psi indicates an evaporator temp around 54f. Yet you get vents in the 61f range. Air bypassing the evaporator or mixing with air passing over the heater core will cause that.

Where is the TXV mounted? Can you reach it without taking anything apart?

[DetroitAC]

Jaz, does the system have a TXV?

What do you mean by a modern York? It's like a modern Packard or Studebaker?

What kind of condenser is it? Does it cycle the clutch based on pressure? Or based on evaporator temperature?

[bohica2xo]

DetroitAC:

The Interceptor was often described as a "Greenhouse"


They used 383 Chrysler engines and 727 Torqueflite transmissions.

I would guess the York was considered "modern" in a land where beam type steam engines were still in use when they built the cars...

It should be a TXV system with an evaporator temp sensor for cabin temperature control

[Jaz]

Thats a modernised rebuild with an LS engine and modified throughout.
I like to keep mine almost standard with a few subtle and mostly hidden upgrades.

To answer some of the questions and advice given.

I will take readings again although its now colder here in the UK, 20c is average in summer but now dropped as storm has come in.
I took previous readings idling at 700rpm and then higher rpm so this probably is where the pressure changes come in, when I next check I will set idle to 1500rpm as advised.

I do know the charge weight and maybe this is the way forward to carry out a full evacuation and recharge, this would raise another question though. Would I need to add more oil and if so how much after a full gas recovery (I would have to get this done elsewhere though as it would not be worth me investing in the equipment for this.

The TXV is easily accessible in the engine bay.

The compressor was new 8 years ago and I believed it was a modern copy of the original York compressor. It does look exactly the same, the clutch is controlled by a stat in the evaporator.

As soon as it warms up I will bet more readings, although based on our relaivly low temp in UK it would seem not to need ac these cars suffer from huge heat soak from a big block engine squeezed into a small hole then the addition of lots of glass, they can get bery hot even at 20c.

[bohica2xo]

Must have been fun fitting the York to an LS. It is much easier to swap a V7 on to the original 383.

If you can touch the TXV with it running, check the line between the TXV and the evaporator, It should be cold. Then check the suction line where it leaves the evaporator case. They should be very close to the same temperature.

[Jaz]

Ive done the test again taking note to keep the engine revs at 1500rpm.
You will see the high pressure rise and fall as the trinary switch signals the fans, this is part of the design and is in the installation notes on the system.

I have made a short video of the test and from my very limited knowledge I would say that either it needs more gas or the TXV valve is faulty. From the chart I have I thought I should have seen around 50PSI on the low side.

https://www.icloud.com/iclouddrive/0IxT ... w#IMG_7828

On another note my daily driver which I have not had long and took to my ac “specialist” who connected it to his big machine and pumped in some gas, im not sure how much he put in but he got the temp at vent to 8c. I noticed though he compressor cycles on and off a lot so I put my gauges on and got static pressures low 78 high 70 the outside ambient was 24c.

When running though the low stayed at 25psi but the high went up to 430psi and then the compressor cycled very quickly cutting out I presume because the pressure was way too high then back in as it lowered.
Im thinking this could be a faulty fan or blocked condenser.

Just my thoughts and im eager to be taught more on this subject. I have had to start doing this myself as living fairly rural there is only one specialist and he doesnt seem to take the time to do the job properly even though he has all the equipment.

Thanks for all your help.

[DetroitAC]

Jaz,
Do you know what the engine to compressor drive ratio is to your York compressor and the displacement of the York? I could do some research on the York to find out, but maybe you or somebody else knows?

It's really fundamental (to me, I guess) to explain how big the compressor is in actual RPM vs suction gas displacement. Can you imagine someone buying a normally aspirated car from the 70's and not asking how big the engine is? Is it a 1.0L 3 cylinder or an 8L V10? It's a big difference! Is your compressor moving 50cc suction gas per rev or 300cc? It's a big difference!

How about the quantity of airflow coming from your HVAC unit? Do you have any way to measure or estimate it? Do you have a comparison to some other vehicles?

The sightglass on you receiver is a very useful tool, I wish every modern car had one, (Toyota likes them) we ALWAYS try to run subcooled, at high loads we will typically have about 10K subcooling, at lower loads having subcooling isn't always possible and a bubbly liquid line is OK. If you can test in high loads you should at a minimum add charge to get clear liquid in the sightglass. Not sure if you will be able to get the loads high in the UK, but at your normal "high" load conditions, whatever those are, you should charge until you get a clear sightglass. I can't advise about any more charge and more subcooling as I have no idea how your condenser is constructed. I can tell you there is no downside to charging up to a clear sightglass at high loads.

How about the evaporator exit pipe (suction pipe) temperature and pressure? Do you have any way to measure? If you do have a way, I can suggest ways to get a somewhat accurate measurement. I do this for a living and I use 3x RTD probes calibrated accurate to 0.1C immersed in the refrigerant for ~100mm. I also don't work on any refrigeration system without having my hands on the pipes, it can tell you a lot, but actual measurements are much better.

[tbirdtbird]

" I can tell you there is no downside to charging up to a clear sightglass at high loads."

Detroit, this is interesting. We have always been told otherwise. What about a critically charged modern system, if it had a sightglass?
I am confused. None of my 134 systems that we install have a clear glass, in fact, there is a sticker over the glass so you can't even see it, unless you deliberately look. I am told it is there should you be running R12, peel the sticker off.