360 AC Problem, High Low Side & Low High Side

Hi Fchatters,

I was experiencing mediocre AC performance in hot weather and decided to read the high and low pressures on my 2000 360 Modena. I would like to ask for your help & suggestions for potential fixes and whether or not I can DIY this repair.

Conditions for gauge reading:

• 80F environmental temp
• idling for 10 minutes
• fan speed: III (max)
• temp setting: low
• vent direction: auto

Measurements:

• High side = 160 psi
• Low side = 50 psi
• vent temp = 60F (taken with IR heat gun)

Specified Pressures in WSM: 29/195 PSI after ten minutes on max cooling

Observations while using Auto Temp Mode
When I put the temp setting to "auto", the right radiator fan will cycle on and off every 1-2 minutes. High and low pressure readings also cycle from 150-190psi 45-50psi, respectively. Watching the gauges with fan off, the high side pressure slowly climbs until the fan turns on. For the first few minutes, the fan would turn on when the high side reached 190-200. Later, closer to ten minutes, the fan would turn on when the high side reached 175-180F. The fan would remain on until high side dropped to 150psi. At this point, the fan would turn off and would turn on again when pressures were as previously mentioned. Seems like normal behavior for the auto mode? With the temp setting set to III, the fan is always on.

Diagnosis
Based on some google searches and reading in the forum, I believe I had a stuck/faulty expansion valve. This seems to be the most common failure for the symptom of "high low side pressure and low high side pressure." Although the part isn't super expensive, it requires removing the dashboard to replace it. I literally just did this last week to install new vents and fix some leather issues. I don't really want to pull the dash again.

Vehicle History

• AC compressor was replaced in mid 2018 after the car was in storage for 5-6 years

Potential Fixes without Dash Removal. What do you guys think of these options?

• replace the filter/dryer
• bake the original filter/dryer in the oven
• flush the AC system with solvent as described by this thread (link)

Last question is, should I avoid using my AC until it is repaired? I don't want damaging the compressor or any other parts.

Thanks,
Ken

 

I dont know much about A/C and how they work but all I know is on my 360, F430 and now my 2016 California T the dang air conditioner and heater is pretty much On or Off operation even in auto mode. It is not like my BMW where you can set the temperature on 70F and it will actually try and maintain that temperature.

 

The symptoms you describe sounds like ones you mentioned could be a weak compressor

Do this test .. try putting ac on the lowest setting with recir on and close the doors .. monitor the pressures and temps on vents etc

Also monitor the compressor cycle

Just another thought ..could your blend doors be stuck since you had dash out.... If you have a good diag tool you may be able to get a evap temp ...can you feel the return ..is it coldish

Let me.know those results



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If it was a weak compressor, you would not be getting the pressures. It is getting a low pressure and giving out a high pressure so it is doing what it should

The expansion valve is probably ok, if it was blocked you would be getting no flow through it and no cold outlet air- the compressor would pump down the suction side until it cut out on low pressure ( LP cutout switch mounted on top of the drier ?)

To check the condition of the drier, feel the temp of the inlet and outlet- they should be the same, if the outlet is colder than the inlet then it is dirty. The liquid refrigerant is expanding over a restriction

Generally only reason the expansion valve can be restricted is if the drier is not doing its job and you have moisture in the system, you then get ice forming in the valve.
Pointless baking drier in the oven, if its that bad then replace it- drying it does not clean out any dirt trapped by the fine mesh screen in the inlet side.

 

The reason I mentioned weak compressor is that low side is high and high side is low which is a sign of a weak compressor

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If the system has any isolating valves you should be able to shut off the liquid line, bypass the LP cutout switch and pump the suction pressure down to about 10 psi, this will prove the compressor. Try pumping down anymore and it will draw air in.
If you think the suction pressure is high, it might be the low pressure switch is defective, so it is cutting out too soon. The greater the range between suction and discharge pressure, the greater the expansion effect over the exp v/v and the colder has for the evap.

 

The quick test I mentioned above should shed some light .. I asked to look at clutch on compressor if cycling and with the low demand if it cools it will give us more direction

As with everything not having car in front of me ..very hard ..but let's not discount blend doors as well ..

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Thanks for the responses and suggestions for further diagnostics. I'll do some more testing today and get back later tonight.

@flash32 I'll run the system on the lowest temp setting, max fan speed, recirc on and try to check the things you mentioned. My undertray is off and the car is on a lift, so I'll be able to feel and measure the temp of the return line between evaporator and compressor.

What did you mean by "blend doors" might be stuck? Do you mean the five vents on the dashboard may be closed?

I haven't heard the compressor short cycling in my test yesterday. I think it stayed on the entire time (20 minutes total at idle) even though the condenser fan was going on and off in "auto" fan speed mode.

@mike32

I will run the system again today and measure the inlet/outlet temps at the dryer filter. It is the original 20 year old filter per the service records, I ordered a new one last night and will be replacing.

I don't think the system has any isolating valves that I can shut off, at least not that I'm aware of. I don't know much about low pressure switch and will have to learn about that some more to diagnose it.

I agree that I think the compressor is working well. I don't hear short cycling, and it is able to compress the gas from 50psi to a higher value (190-195 measured on the high side).

 

Use lowest fan setting and lowest temp setting for the test

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@flash32

Gotcha, I'll check the compressor for cycling while on low demand. What's the desired result in this test?

I believe the 360 system uses the TGK valve to control temperature settings. Don't think it also has a "blend door" to control airflow. I do have the ability to control the temperature setting from hot to cold, so I believe that is functioning. I can also hear the motor actuating when I turn the temperature dial.

 

The motor you hear is what I call the blend door .. mixing heat and cold .. it has been a known issue that the motor goes and although ac is working it continues to blend hotter air with the cold .. I think there have been a few people who had that issue


The desire result would be a cycling compressor and pressures that look good and cold evap



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Yeah, I know I can test the TGK / blend door by manually opening and closing it with a 9V battery. I can test the AC again w/gauges connected with the TGK manually set to cold.

 

The tgk and the flaps / blend motor are two different things .. the tgk controls coolant flow ..the part I was speaking of blends air ..I attached the pic Image Unavailable, Please Login

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I ran the suggested tests today and gathered temperatures at the compressor inlet & outlet, and also the dryer filter inlet and outlet. The fan was cycling on and off in all the tests today (trials 2-4). This made it difficult to pick a single high and low reading, but for a couple of the tests I felt the pressures stabilized even when the fan cycled on and off and recorded those values.

The fan only stayed on, constantly in trial 1 from yesterday. Which was recirc off, low temp, fan speed III (max settting).

Please let me know what you think of these measurements (image attached). There's also a link to the google sheet if you'd prefer to make comments on the sheet or make a copy to do any calculations, etc.

https://docs.google.com/spreadsheets/d/1DJoHfNmGfy_Ljezjw9TjuEcAnpD5yKr6gAN1kuIeidY/edit?usp=sharing
Image Unavailable, Please Login

 

I cant help on this blend door system as never looked at it, but the theory is that it allows the system to supercool the air so the humidity drops out as condensate, the air now being too cold for comfort is reheated by blending in warm air. Result is dry warmer air.

 

On top of the drier you might find a pressure switch with 2 wires, this is the low pressure cutout, if you lose too much gas this stops the compressor from running and damaging itself.

 

Nice spreadsheet

After looking at this for a long while I am starting to wondering the accuracy of the low side gauge

Maybe you can connect the high side gauge to low side port by flipping hose on manifold (only do this for high side gauge ) and see if still 50 psi

And actually before you do that .. give us a static temp and pressure read at rest

From my analysis I see negative subcooling and way high superheating going based on your spreadsheet which all would point to low refrigerate except for the high reading in low side .. which makes me second guess the gauge

Let me know because maybe all all you need is to evacuate and refill system with exactly the right amount of refrigerate and while you are at it change dryer

Btw if you are low on refrigerate it would mean you have a small leak .. so consider a dye when refilling it after evacuate

Please post standing / static pressure and ambient temp and also if low pressure when using high side gauge is still ,50 psi

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@flash32 Thanks again for the reply, awesome feedback.

I already had engine off readings at room temp. On both days it was LP 80 and HP 75. That's interesting because my understanding is that it's supposed to be the same. So that suggest maybe my low side gauge is reading higher than the high side. I will try using the high side gauge on the low side port like you suggested to see if I can determine if my LP gauge is bad.

Might have a small leak where the condensor lines attach. I can't get to them right now even though the wheel well liners are off. I think I need to remove the front bumper to get to those connections? I've sniffed all other connections and don't sense leaks.

Anyone know why my compressor clutch doesn't disengage while the AC is running for 20 minutes? Should it normally disengage during a long period like this?

 

I thought I knew the answer to this but wanted to double check by asking Google.

https://www.google.com/search?q=when+does+a+car+ac+compressor+shut+off (when does a car ac compressor shut off)

I'm not faulting you for asking the question, I'm marveling at how good Google is getting at answering natural language questions. I've been using a Google speaker gadget (not sure of the actual name) and asking questions in a more natural way and getting surprisingly good answers. You can ask follow up questions too and the machine keeps the context of the conversation in mind while answering subsequent queries.

The above question returned a very satisfactory and point blank answer. Impressive.

My understanding of the system is that the compressor shuts down when the temperature has reached a steady state.

 

@EastMemphis

Yes, Google is amazing and that link has some good info =). Thanks for sharing it. Maybe I have a bad thermal sensor at the evaporator? Or maybe the evaporator is never reaching the optimal temp b/c the low pressure is too high (and pv=nrt, so higher low side pressure=higher evap temp). I ask the same questions here to see if anyone with Ferrari experience has more specific answers and common failure modes for our cars. It's interesting that my clutch is never disengaging. I'll know I can turn the AC off by pushing the "stop" button, I'll verify the clutch disengages when I do that later this evening.

I've got a dehydrating filter and pressure switch on order. I will replace both of those when I evacuate the system, refill, and then see how things work after a fresh refill. Debating whether or not to hire an AC specialist to empty and fill the system OR to buy the Robin Air R3 recovery system for $430 off Amazon. Seems like the recovery system will easily pay for itself in a few years since it can be used for auto and home HVAC systems. I also love learning new stuff and having the ability to service things on my own.

 

If my theory proves out about gauge reading too high and in fact you have low pressure on lp side.. I would add a little refig to test if temp changes ..if so I would then evacbsystem and refill properly

In terms of compressor .. I am not sure if the case with the 360!..but modern variable compressors stay on always once ac switch is on .. the variable compressor changes suction/pressure internally.. but again I don't know off hand if the 360 uses fixed or variable compressor




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Hey Flash. So I measured the low side pressure using the high side gauge. I got the same static pressure reading of 80psi. Suggests there's nothing wrong with the low side gauge.

I'm not sure if the compressor is variable or fixed. However, I noticed whenever the condenser fan turns on, the high side pressure drops a lot, often going from 175-180PSI down to 150PSI. I believe this drop is caused by the compressor turning off? So, it must be turning off somehow even if I don't see the clutch disengage.

Also, I verified the clutch disengages with the AC is turned off.

 

Measure the low side with car running .. I am hopefully you are going to be lower the 35 hence a low refrig condition..

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The drop in pressure is most likely the cooling effect of fan on condenser which cools the liquid refrigerant down to according to your pressures about 112 degrees

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Doing some other searches, it sounds like the standard practice for measuring AC pressure is to have the engine at 2000 RPM and to use a fan blowing on the condenser the whole time. I have been at idle and no fan, so I will do another test with the engine at 2000RPM after ten minutes of idling + standalone fan.