AC Issues : Denso Compressor Pressure Not Correct (1 Viewer)

[jayfrem]

Hi There

My AC is not blowing good COLD air.
About 2 years ago we changed the evaporator and last year we changed the compressor.

I went with a brand new Denso unit off amazon ( Part 471-1220).

Went to the AC shop today and it the compressor is showing higher pressure at idle. It tends to cool better when RPM goes up.

We are doubting the compressor but strange thing that is newly installed.

We vaccumed the system and refilled.

There is no leaks in the system.

Some improvement but not much. The truck always needed 2-3 min to start blowing cold air if it was parked and your cranked it on and turned AC on.

Can you advise where else to look before attempting to try another compressor ?

Jay

 

[TXSunDevil]

When you say pressure not correct do you mean high suction pressure while running? Did you change the fan clutch? Does the pressure change in the 2-3 minutes before it starts blowing cold?

 

[jayfrem]

When you say pressure not correct do you mean high suction pressure while running? Did you change the fan clutch? Does the pressure change in the 2-3 minutes before it starts blowing cold?

High pressure on the AC machine while idle. When you increase the RPM it starts blowing cold.

Attached is the compressor bought from Amazon

https://www.amazon.com/gp/product/B001UCBMJK/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

No the fan clutch was not changed.

Where to look ?

 

[TXSunDevil]

I am sorry I meant clutch changed and yes it appears that compressor comes with a clutch. There are two pressures on an ac system. The high or "discharge" pressure and the low or "suction" pressure. We need to know if it is a high pressure on the low or the high side while at an idle. High suction at an idle is different than high discharge at an idle. They both have different causes.

 

[jayfrem]

I am sorry I meant clutch changed and yes it appears that compressor comes with a clutch. There are two pressures on an ac system. The high or "discharge" pressure and the low or "suction" pressure. We need to know if it is a high pressure on the low or the high side while at an idle. High suction at an idle is different than high discharge at an idle. They both have different causes.

It is a high side at an idle.

Pls advise.

 

[TXSunDevil]

Usually with a high side high pressure I would look towards a blockage in the metering device or possibly non condensible in the system. With high pressure on the high side I would not think a compressor would be the issue. Did your evaporator come with a new expansion valve or was it changed with the compressor?

 

[flintknapper]

We simply need more (and accurate) information.

Are you saying the gauges showed a 'high' high side pressure only? (low side was normal)?

Give me a figure here, what pressure are they saying is 'high' and what was the ambient temperature when they tested it?

Is your Fan Clutch working properly?

At any time during all of these exchange/services (replace evaporator, replace compressor, evac and refill that was just done) was the drier (or desiccant pack) ever replaced?

Was the TXV replaced when the evaporator was done?

What are your actual vent temps?

IF the A/C shop just evacuated your system, refilled and shoved you out the door without any pre-work diagnosis, I would not be going back to them.

 

[jayfrem]

Usually with a high side high pressure I would look towards a blockage in the metering device or possibly non condensible in the system. With high pressure on the high side I would not think a compressor would be the issue. Did your evaporator come with a new expansion valve or was it changed with the compressor?

Hi There

It is a high low side.

Pls advise

Jay

 

[flintknapper]

Hi There

It is a high low side.

Pls advise

Jay

In your post #5 you indicated it was a 'high side', now you are saying its the 'low side'.

??????

We would love to try and help...but we need accurate information. And frankly MORE information.

Please go back to my post #7 and answer those 'important' questions for us.

Diagnosing A/C problems over the internet is hard enough. It becomes an absolute guessing game without certain information.

 

[jayfrem]

In your post #5 you indicated it was a 'high side', now you are saying its the 'low side'.

??????

We would love to try and help...but we need accurate information. And frankly MORE information.

Please go back to my post #7 and answer those 'important' questions for us.

Diagnosing A/C problems over the internet is hard enough. It becomes an absolute guessing game without certain information.

I confirm it is a high “ low side”.

I do not have the readings.

Jay

 

[flintknapper]

I confirm it is a high “ low side”.

I do not have the readings.

Jay

OK, since we aren't going to have anything more than vague information to go on....I will offer you this.

IF the low side reading is high (High side normal) then most often... this points to excessive flow of refrigerant through the evaporator. Meaning your TXV is stuck 'open' or the sensing bulb has an issue.

Personally, I think you have an air flow problem and a 'failing' TXV, but without benefit of more information its only a WAG.

I'd be curious to know what excuse the A/C shop had for letting you leave without either fixing the problem or conferring with you about it.

I doubt your compressor is the problem. My advise would be to take it back to the shop or choose another shop and get a second opinion.

Unfortunately, we will not be able to help you here based on scant information or symptoms.

Please let us know how it works out....so others might benefit from it.

 

[jayfrem]

OK, since we aren't going to have anything more than vague information to go on....I will offer you this.

IF the low side reading is high (High side normal) then most often... this points to excessive flow of refrigerant through the evaporator. Meaning your TXV is stuck 'open' or the sensing bulb has an issue.

Personally, I think you have an air flow problem and a 'failing' TXV, but without benefit of more information its only a WAG.

I'd be curious to know what excuse the A/C shop had for letting you leave without either fixing the problem or conferring with you about it.

I doubt your compressor is the problem. My advise would be to take it back to the shop or choose another shop and get a second opinion.

Unfortunately, we will not be able to help you here based on scant information or symptoms.

Please let us know how it works out....so others might benefit from it.

Attached few pics. Temp is C.

10 C = 50 F
8 C = 46.4 F
12 C =53.6 F

Is this normal when driving RPM above 2000 for compressor to cool better on these trucks ?

The serpentine belt is what drives the compressor i believe.

 

[flintknapper]

Per your pics the best I see is 11° C. Which is approximately 52° F.

Whether or not that is a normal/desirable vent temp depends on the ambient temperature.

IF it were 100° F. outside with the sun shining in your windows...then I'd say YES, I would be quite happy with 52 degrees (48 degrees below ambient).

Conversely if it were only 80° F. ambient (outside temp) and you are getting at best... 52 degrees at the vent (engine rpm 2K), then I'd say you have room for improvement.

Just as a rule of thumb: A well working auto A/C system should be able to provide a minimum of 30° F. temperature drop (at the middle vent) from the ambient temp. More common is a 35 degree drop and if you can get a 40 degree drop...then you should be quite satisfied.

Having said that..there are many things that influence the ability of your A/C system to cool efficiently.

But the primary two are: Proper refrigerant charge and AIR FLOW through the condenser.

And yes sir, the serpentine belt drives the A/C compressor.

 

[jayfrem]

Per your pics the best I see is 11° C. Which is approximately 52° F.

Whether or not that is a normal/desirable vent temp depends on the ambient temperature.

IF it were 100° F. outside with the sun shining in your windows...then I'd say YES, I would be quite happy with 52 degrees (48 degrees below ambient).

Conversely if it were only 80° F. ambient (outside temp) and you are getting at best... 52 degrees at the vent (engine rpm 2K), then I'd say you have room for improvement.

Just as a rule of thumb: A well working auto A/C system should be able to provide a minimum of 30° F. temperature drop (at the middle vent) from the ambient temp. More common is a 35 degree drop and if you can get a 40 degree drop...then you should be quite satisfied.

Having said that..there are many things that influence the ability of your A/C system to cool efficiently.

But the primary two are: Proper refrigerant charge and AIR FLOW through the condenser.

And yes sir, the serpentine belt drives the A/C compressor.

Thank a lot for the help.

Here are the temperatures

Air Temp 6.5-8 C or 43.7-46.4 F at more than 2000 RPM ( open traffic) and Ambient of 34 C ( 93.2 F )

Air Temp 12-14 C or 53.6-57.2 F at less than 2000 RPM ( Traffic or idle ) and Ambient of 34 C ( 93.2 F )


We cleaned the AC radiator and changed its filter.

Since the Compressor is driven by serpentine belt is it normal that it will be more effectively at higher RPM ?

Is it normal to see a difference of 10 F in air temperature between highway driving and idle ?

This is mechanically driven compressor wondering if it is the same type of the newer LC 200 ?

 

[jLB]

The other contributing factor, for the AC being less efficient at idle, is the lack (lower volume) of airflow through the condenser

 

[flintknapper]

Thank a lot for the help.

Here are the temperatures

Air Temp 6.5-8 C or 43.7-46.4 F at more than 2000 RPM ( open traffic) and Ambient of 34 C ( 93.2 F )

More than acceptable.

Air Temp 12-14 C or 53.6-57.2 F at less than 2000 RPM ( Traffic or idle ) and Ambient of 34 C ( 93.2 F )

I'd say this is working fairly well (36° F. below ambient).

We cleaned the AC radiator and changed its filter.

I'm guessing you mean the Evaporator inside the vehicle and changed the Cabin Air Filters, good!

Since the Compressor is driven by serpentine belt is it normal that it will be more effectively at higher RPM ?

Of course. Higher rpm means more refrigerant circulating through the system at a faster rate than lower rpm, hence more cooling. But its important to understand how your A/C unit works. It isn't designed to pump cool air into the cabin, it removes the heat (and humidity).

Is it normal to see a difference of 10 F in air temperature between highway driving and idle ?

Close to that. Again...lower rpm means the compressor is not working as hard. BUT there is more to it than that. AIRFLOW through the condenser (located right in front of your radiator) will determine how well your system can shed the heat. If all else were perfect with your system, if you don't have good air flow you will NOT have good cooling and I suspect this is your problem or at least an area than can be improved.

If the vehicle is the '99 LC in your signature line, then it should already have a 'Aux Fan' to help with low speed cooling. BUT check your fan clutch as well. If it isn't working properly...then it isn't pulling as much air through the A/C condenser, your radiator... and then blowing across your engine. This will hurt performance in all those areas. At highway speed you should be OK but at low speed a STRONG, properly working fan clutch is essential.

This is mechanically driven compressor wondering if it is the same type of the newer LC 200

We don't care...unless you plan on moving up to a 200 series.

?

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[jayfrem]

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Flinknapper

Thanks a lot for your response.
Toyotas are known for great cole AC s .


Once again my problem is less AC coolinf at lower rpm.

Th AC electrical fan is working when AC is on.


What to check in the AC fan clutch as per your reply ?

The Denso compressor i used has the following Denso part #
471-1220

 

[flintknapper]

Flinknapper


Toyotas are known for great cold AC s .

Yes, when working properly.

Once again my problem is less AC cooling at lower rpm.

Perfectly normal...as discussed in a previous post.

Th AC electrical fan is working when AC is on.

Good, so we know your Aux Fan works, your Trinary switch works and that you have at least 180-220 psi pressure on your high side line.

What to check in the AC fan clutch as per your reply ?

*****Read This**** Your 'Fan Clutch' is designed to engage (partially or fully) as needed and drive the plastic fan which pulls air through your A/C condenser and radiator and then blows across your engine and transmission. It also aids in evacuating heated air from the engine compartment (at ALL traveling speeds) but in-particular during low speed travel or while the vehicle is stopped.

I can't stress enough how important it is to have a properly working fan clutch. IF yours is the original or is many years old...I wouldn't even bother checking it. Replace it. You can read up on how a fan clutch works...I won't take up everyone's time with that. But recognize...it is a VERY important component of your cooling system. I'd bet yours is weak.


The Denso compressor i used has the following Denso part #
471-1220

^^^^^ That's fine.

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[jayfrem]

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Thank you Flintknapper

From your previous you mention it is normal to get an increase of 10 F in air temperature between 2000 RPM and idle.

The fan clutch is still the original one.
How can i test it ?

My low pressure side is still
Showing a bit of a high reading. Pic attached. Got this from the AC shop.

Is my Denso part # inline with OEM specs ?

 

[flintknapper]

From your previous you mention it is normal to get an increase of 10 F in air temperature between 2000 RPM and idle.

It 'can' be normal to see as much as 10°F difference in vent temps, depends on conditions. But certainly within a 'window' I would consider normal.

The fan clutch is still the original one.
How can i test it ?

You can roll up a magazine or newspaper and CAREFULLY/SLOWLY press the end of it against the turning fan blade to see if you can stop or slow it. (DO THIS AT YOUR OWN RISK). If you can..then the fan clutch is not operating correctly and should be replaced. But even you don't stop/slow the fan blade, chances are the silicone fluid inside the clutch has lost its 'shear' capacity and the clutch is not working as well as it should be.

I wouldn't even bother testing an original fan clutch unless you plan to keep it and modify it (change the silicone fluid to a heavier one) which will rejuvenate the clutch and increase it's performance.

My low pressure side is still
Showing a bit of a high reading. Pic attached. Got this from the AC shop.

Doesn't help me without benefit of the high side reading as well. Also need to know the ambient temperature when the reading was taken.

Is my Denso part # inline with OEM specs ?

Your compressor should be fine.

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