Thoughts on my r134a pressure?

[Cranky]

I when back and watched the vid. I never seen a clutch cycle like that. There's something else going on. Please everyone, watch the vid. That double cycle is strange. Almost like two different thing are controlling the clutch.

I noticed that too but thought the vid got paused for a few seconds.....

 

[RJRENTON]

Gentlemen I have an update. I wasn't able to drive the car until today, and while the refrigerant pressures are still great the compressor was clicking on and off again, a lot. But when I jump the terminals on the switch at the dryer the compressor runs constantly (as it should) and the cabin begins cooling off.
Unless I'm on the wrong track, I'm going to try the switch next, It looks like a regular parts store switch, nothing special.

View attachment 980590

IMO...
The switch action is Normally Closed and Opens on pressure fall. The range of the switch between open and close is called the dead band.....and applies both ways.... closed to open and reclose. Typically the switch is mounted on a Schrader valve type fitting, that, upon removal seals itself off, similar to a tire valve. USUALLY, the switch's calibration adjustmet is inside the mounting stem. I've adjusted this switch to open (turning off the compressor clutch coil) at a slightly LOWER pressure, yielding a colder evaporator pressure and colder air off the coil.....maybe 3-5 psi lower pressure will yield 5-10° lower temperature....tbd empirically...trial and error.
This switch is NOT to be confused with a HIGH pressure switch that protects against high pressures. This high pressure switch is Normally Closed and OPENS at high pressure....perhaps in 250-275 psi range...turning off the compressor clutch coil allowing the pressure to fall. The system's high pressure relief valve is in addition to this switch....the high pressure relief valve is usually set to open at 1.5x normal maximum pressure...say 300 psi. Just my opinion of course.
BOB RENTON

 

[Demonic]

Don't "try" anything, untill you post the suction and discharge pressures with the switch jumped out and the rpm at 1400-2000. The dryer is on the high pressure side, unless the orifice is at the end of the condenser, or it is a compound switch (unlikely).

 

[RJRENTON]

Don't "try" anything, untill you post the suction and discharge pressures with the switch jumped out and the rpm at 1400-2000. The dryer is on the high pressure side, unless the orifice is at the end of the condenser, or it is a compound switch (unlikely).

The system layout can be different for each manufacturer/model of vehicle. For example, the receiver/accumulator (which contains the dessicant) on my 2020 yukon Denali is on the evaporator outlet. The system also uses a suction pressure switch AND a thermostatic expansion valve (TXV) on the inlet to the evaporator and a variable displacement axial flow compressor. The system produces approximately 38° air flow without cycling the clutch. As the suction pressure drops (due to low demand), the compressor displacement is reduced and the TXV throttles the refrigerant to the evaporator's inlet to prevent icing during high humidity low inlet air temp conditions.
What value is in the "posting of the suction and discharge pressures" with the pressure switch jumped out and at 1400-2000 RPM ..... (engine or compressor rpm)?. If the metering orifice was st the end of the condenser, the phase change will occur at that point.....the refrigerant metering orifice is at the INLET to the evaporator to allow for the phase change of the liquid refrigerant to a gas (where the liquid "boils" or absorbes heat...the latent heat of vaporization). A refrigerant system does not make cold....it removes heat. I've not seen a compound action switch for that application...but it may be possible.
BOB RENTON

 

[JerseyJoe]

Don't "try" anything, untill you post the suction and discharge pressures with the switch jumped out and the rpm at 1400-2000. The dryer is on the high pressure side, unless the orifice is at the end of the condenser, or it is a compound switch (unlikely).

Thanks again for everybody's help, strange that the readings have changed so drastically since Friday with no adjustments.
Here you go. 1800 RPM, switch jumped. Low side pressure reads normal and high side was heading North of 400 before I shut it off (manual says switch range is 30-406 psi). The dryer with binary switch is mounted on the high side, the part number matches a pretty common switch: https://www.summitracing.com/parts/...ObJgRBd1RplJk6e5YesULhe1Iq7HeOiRoCPqgQAvD_BwE

 

[1 Wild R/T]

@ 400 PSI either your overcharged or the ambient temperature is around 140.... Good thing it cycled to protect the system....

How is airflow across the condenser?

 

[JerseyJoe]

@ 400 PSI either your overcharged or the ambient temperature is around 140.... Good thing it cycled to protect the system....

How is airflow across the condenser?

I'm going to pick up a large fan in the morning and try this again. Not much air was moving when I shot that.

 

[1 Wild R/T]

Your engine driven fan (assuming you have an engine driven fan) should move enough air to keep the head pressure down..

 

[Beekeeper]

Did you add oil to the system?

 

[JerseyJoe]

Did you add oil to the system?

The compressor came oiled but I did vacuum out the system before I charged it last week. I did not add more.

 

[Beekeeper]

The compressor came oiled but I did vacuum out the system before I charged it last week. I did not add more.

Ok should be good then too much oil can cause the the high side to be too high. Do you have a clutch fan? as R/T stated you may not have enough airflow across the condenser.

 

[JerseyJoe]

Ok should be good then too much oil can cause the the high side to be too high. Do you have a clutch fan? as R/T stated you may not have enough airflow across the condenser.

I have a 17" electric from Rainbow Products. The controller has the override that puts it on high speed with the A/C.

 

[Demonic]

What value is in the "posting of the suction and discharge pressures" with the pressure switch jumped out and at 1400-2000 RPM .

The point is, to get a steady state reading with the refrigerant settled out. Refrigerant will always migrate to the coldest point in the system with the compressor off. Often this is the evaporator. Good practice requires several minutes of the compressor running steadily to determine what is going on.
So, several of us, myself included, figured he was under-charged. But now, seeing where the switch is physically located...oh boy. So it is a compound switch, or "binary" as the mfg noted in the Summit link. Good, protection for both conditions...Still somewhat hard to pinpoint without knowing the ambient temperature. I should have looked at his location closer. So it's been murderously hot in S. Jersey. You're only a little overcharged, or there's air in the system The TXV is doing it's job, trying to maintain the right evaporator pressure. your binary switch is likely tripping on HP, protecting the system. Likely overcharged. Common, but now it's tricky to correct. Too easy to recover too much and be undercharged without a refrigerant scale, time, and a little patience. Bleed off briefly from the liquid side till you get to 375 psi discharge.

@ 400 PSI either your overcharged or the ambient temperature is around 140.... Good thing it cycled to protect the system....

Agreed. Get a big box fan or something. I would weigh the charge back out about 4 oz at a time and see where it settles out, unless increasing airflow drops that discharge pressure about 50 psi. Those pressures are close if it was about 105*F where the car was at the time. I like the override feature on your fan. Still, it shouldn't hit the high switch setting unless something is amiss.
You can't weigh a charge out into a recovery can without a good refrigerant scale, careful setup, and a bit of precision. Commercial HVAC tools.

 

[RJRENTON]

In an A/C system, with the compressor off, the system's pressures will tend to equalize in the evaporator, condenser, dryer, all components, etc. Upon compressor re-energization will begin the system pump down to create the high-low pressure gradient across the system's metering device (orifice tube, capillary, or TXV) and establish the Carnot cycle's pressure-temperature-liquid-gas phase relationship. Air in the system will definitely cause high discharge pressures as well as too much oil and inhibit the condensing of the refrigerant, as air is considered a non-condensible and will accumulate at the top of the condenser.
Please explain how a "binary" switch operates....are there 2 different set points with only one set of contacts? The switch shown has only two terminals....how can this supply both high and low pressure set points and what is the dead band range and is it adjustable? I'm dubious...
BOB RENTON

 

[66chargerpat]

One easy way to tell if you are moving good air through the condenser, is check the temp. at receiver dryer. The dryer needs to be cool enough to hold your fingers on it.

 

[JerseyJoe]

Agreed. Get a big box fan or something. I would weigh the charge back out about 4 oz at a time and see where it settles out, unless increasing airflow drops that discharge pressure about 50 psi. Those pressures are close if it was about 105*F where the car was at the time. I like the override feature on your fan. Still, it shouldn't hit the high switch setting unless something is amiss.
You can't weigh a charge out into a recovery can without a good refrigerant scale, careful setup, and a bit of precision. Commercial HVAC tools.

I stopped here, before I add any more to the system. It's 95 degrees outside, I pulled a big belt driven fan out of the attic and there's plenty of air moving! Pressures look low to me, judging by the chart and the ambient temps. Vent was steady at 50 degrees. I'm assuming my next move is bring the pressure up to spec and see if the compressor stays engaged? The video shows the rapid cycling it was doing before.

 

[66chargerpat]

From that vid. it appears to be cycling on high discharge pressure, not from low suction pressure.

 

[Demonic]

Agreed with post above. Your discharge pressure is way too high. Either air still in the system - seems unlikely with a good evacuation, good gauges and hoses - or you're overcharged, as I said earlier. You'll never cool correctly cycling the compressor like that, and eventually something will give up from short-cycling.

Your high side pressure should be around 275-300 psi at the most. But the system cannot settle running like that. Post #45 - your suction pressure is good, but the discharge is too high. 345 is the limit.

Remove a little, about 4 oz to start. Set your idle rpm at 1100 temporarily for a "real world" operation. I'll bet the discharge air temp drops.

https://www.summitracing.com/parts/...ObJgRBd1RplJk6e5YesULhe1Iq7HeOiRoCPqgQAvD_BwE

So the switch is open below 30 psi, closes above, then is open again at over 406 psi. Nice. Matches 134a fairly well. I would add a time delay, so it wouldn't short cycle.

 

[RJRENTON]

Looking at the link for the binary switch, its use is insure there is refrigerant in the system (normally open closes at ~ + 30 psi and remains closed) AND IF located in the liquid line or compressor discharge line, it could function as a high pressure switch (closed and opens on high pressure above 300 psi) opening clutch coil supply...not truely a binary control device but simply a dual set point device. However observing the video, the compressor clutch releases momentarily (perhaps 1/2 second) then re-engages; the system is acting like the TXV or evaporator's refrigerant inlet metering device is clogged or otherwise restricted....not overcharged OR if there is a liquid line dryer, it may be restricted internally preventing a steady state supply of the refrigerant to the evaporator, backing up the pressure thru the condenser discharge.
BOB RENTON

 

[Blewmenee]

Before I evacuate the system and start fresh, can anyone comment on my compressor seeming to cycle on and off so much?
Vintage Air recommends 6-18 psi steady. https://www.vintageair.com/tech-topic-troubleshoot-system/#:~:text=Acceptable operating pressure ranges for,PSI in a steady state.

Here's a vid of my system at about 15 psi when the compressor is running, high side was within range at around 200 psi in 90 degree heat. Center vent temp has me thinking air in the system... Thanks in advance

I have a 69 roadrunner with factory air that is all updated from classic out of tampa. My system said 24 oz only(2 cans). Low side just above 20 and 40 degree out vents on 90+ day