1. Very rarely do i hear of the low pressure switch going bad. Can they??
2. Will the low pressure switch completly prevent the a/c compressor clutch from engaging if the switch was faulty?

I was just curious before i shell out money for a new compressor. Went to an a/c shop earlier today to get some things check out. They evac'd the system and put it under vacuum, and it was holding around -30(psi i guess). The tech said that was good. During the recovery process he said they only recovered about .75lbs of freon. He said there needed to be about 1.75lbs. Which even then i don't know is right because the sticker under the hood says 34 oz which is about 2.12 lbs.

Problem: A/c compressor clutch engages but does not blow cold cold air. It does not blow hot air either. Its almost on the verge of semi-warm air but not enough to make me sweat.

So the tech adds the necessary freon. The readings on his machine if i remember correctly were around 30ish on the low side and about 220ish on the high side. He said the readings were a little low. He proceeds to add more freon, i get a little wide eyed because he puts almost 3lbs of freon on. Now when he did that the air did get a little bit colder and the pressure readings did rise a little. But only a little. He said the readings were still a little low.

Anyways, looking for any input. Thanks

 

 

First off, I'm a hvac tech. I do industrial/data center ac's. I've never fixed a car ac because it's removed from my hatch. I got the honda shop manual here.

1. The low pressure switch opens at 33 psi. If the switch was bad the compressor won't engage.
2. It's a safety feature. Compressors are refrigerant cooled. Low charge=no cooling. Compressors are the same thing as a car motor except it has one cylinder.

Did they install a new drier (thing with sight glass)? If your compressor was going bad the hi/lo pressures would be similar, equal if the valves were done. I think you have an airflow issue or a restriction in the system. I'd start with the fan and go from there. If you have more issues with this let them remove the non-condensables (pull a vacuum), but wait 15-20 min before adding refrigerant. If the low pressure gage rises you got a leak as air is being introduced to the system.

Are the two outside fans working? How about the evaporator fan? Condenser coil clean?
How long was the vacuum pump on the system? Keep me posted.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hb &raquo;</TD></TR><TR><TD CLASS="quote">Did they install a new drier (thing with sight glass)?</TD></TR></TABLE>
yes, actually i installed it before going to the shop along with a new expansion valve and new o-rings.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hb &raquo;</TD></TR><TR><TD CLASS="quote">I think you have an airflow issue or a restriction in the system. I'd start with the fan and go from there. Are the two outside fans working? How about the evaporator fan? Condenser coil clean?</TD></TR></TABLE>
Its wierd you say that, the tech also had a "hunch" about some kind of airflow restriction in the system. Both fans are working properly, and as far as the condenser coil im not sure what that is. I'll have to look in the helms tomorrow when i get a chance.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hb &raquo;</TD></TR><TR><TD CLASS="quote">If you have more issues with this let them remove the non-condensables (pull a vacuum), but wait 15-20 min before adding refrigerant. If the low pressure gage rises you got a leak as air is being introduced to the system.
How long was the vacuum pump on the system? Keep me posted.</TD></TR></TABLE>
Well he waited a good 20-25 minutes after pulling a vacuum before adding the freon. The low pressure gauge stayed at -30psi the whole time. I watched the entire process(just to make sure).

Here is the wierd thing i forgot to mention. As i stated in my 1st post, he added almost 3lbs of freon BUT he did another evac and recovery before i left and the machine only recovered approx. 2.15 lbs of freon. We were questioning where the other freon went too. I mean if after pulling a vacuum and the pressure gauge stays consistant, then that would mean NO leaks, right??

He did put in a UV dye. So i will go back in a couple of days to see if there is a possible leak. Thanks for replying man, very much appreciated.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cjsls &raquo;</TD></TR><TR><TD CLASS="quote">
some kind of airflow restriction in the system. .</TD></TR></TABLE>
i was thinking this too... but since u've replaced everything... this shouldnt be a problem.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cjsls &raquo;</TD></TR><TR><TD CLASS="quote">
Well he waited a good 20-25 minutes after pulling a vacuum before adding the freon. The low pressure gauge stayed at -30psi the whole time. .</TD></TR></TABLE>
this sounds good too.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cjsls &raquo;</TD></TR><TR><TD CLASS="quote">
Here is the wierd thing i forgot to mention. As i stated in my 1st post, he added almost 3lbs of freon BUT he did another evac and recovery before i left and the machine only recovered approx. 2.15 lbs of freon. We were questioning where the other freon went too. I mean if after pulling a vacuum and the pressure gauge stays consistant, then that would mean NO leaks, right??

He did put in a UV dye. So i will go back in a couple of days to see if there is a possible leak. Thanks for replying man, very much appreciated.</TD></TR></TABLE>
hm... ill try and bring my grandpa's gauges this weekend, see if i can help u out a bit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondaZvic &raquo;</TD></TR><TR><TD CLASS="quote">hm... ill try and bring my grandpa's gauges this weekend, see if i can help u out a bit. </TD></TR></TABLE>
sweet. one thing im going to check out this week is the low side line(small copper line). I had trouble putting that one in because it soo oddly shaped. Its possible that maybe a section of the line is kinked. Would that cause these wierd readings though???

 

The condenser is the smaller coil in front of the radiator. It's job is to reject heat like the radiator. Bugs and rocks are common. The more clogged it is the less effective (restricted airflow). Do you have a cover of some sort on the dash? Maybe covering the return air (in the middle of dash)? How is the evaporator (inside) fan?

This may sound stupid but if the gages weren't open then it would read 30" inches of vacuum (meaning he evacuated the hoses).

Any kinked refrigerant lines? Check for chaffing of the lines (rubbed something resulting in a leak)

Added 3 lb referigerant/recovered 2.15 lb. The missing .85 lb is probably in the hoses/manifold.

You may also have a restriction in the system. Verify all other parts are working correctly. If all fails you can disconnect the pipes at the metering device and compressor and backflush the system with nitrogen. Some refrigerant oils aren't compatible and cause the oil to thicken.

UV dye Go to the toy store and buy some bubbles. Pour it on the piping. If it blows a bubble.... I have my own way of doing things

If you open the system up get a another drier.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cjsls &raquo;</TD></TR><TR><TD CLASS="quote"> Thanks for replying man, very much appreciated.</TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hb &raquo;</TD></TR><TR><TD CLASS="quote">
UV dye Go to the toy store and buy some bubbles. Pour it on the piping. If it blows a bubble.... I have my own way of doing things

If you open the system up get a another drier.


</TD></TR></TABLE>

bubbles? hmm.. interesting..

i've heard of denatured alcohol as being a good liquid to flush out the system with.

 

i guess i'll take a look at everything later this week and see what i come up with. <TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hb &raquo;</TD></TR><TR><TD CLASS="quote">The condenser is the smaller coil in front of the radiator. </TD></TR></TABLE>
oh ok, i gotcha. i usually just refer to it as the condenser, so when u said condenser coil just got a little confused.

hey z,
i'm telling you man, this has to be a sign to forget about a/c, buy a new car, and make this my project car. 3x now i've tried to put the a/c back.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondaZvic &raquo;</TD></TR><TR><TD CLASS="quote">

bubbles? hmm.. interesting..

i've heard of denatured alcohol as being a good liquid to flush out the system with.</TD></TR></TABLE>

http://refrigtech.com/bigblu.html I get this stuff for free. I say use bubbles because you probably can't get this. They usually only sell to mechanical contractors. I've never heard of using denatured alcohol to flush a system. Nothing beats nitrogen if you know where to open the system and how to backflush it properly.

 

the reason for dentured alcohol, is because it has no moisture, or gets rid of moisture.. something like that.. i dont know exactly.

which it is ok to have moisture in something that u are flushing a system out with because once u pull a vacuum on it, if its a GOOD vacuum, the vacuum will remove all moisture anyway. but its just a safety precaution thing, i guess...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondaZvic &raquo;</TD></TR><TR><TD CLASS="quote">which it is ok to have moisture in something that u are flushing a system out with because once u pull a vacuum on it, if its a GOOD vacuum, the vacuum will remove all moisture anyway. but its just a safety precaution thing, i guess... </TD></TR></TABLE>

Moisture in an AC system is a big NO NO. Oil + moisture=acid.
Not sure how critical this is in automotive.
For a 115/208/230/460V compressor, acid eats the windings resulting in opens/shorts.
It is possible to to make the moisture freeze when pulling a vacuum. Can't explain this one . I'll get specifics tomorrow.

 

-30 psi is impossible. It was -30 inches of mercury.

Moisture is a no-no for auto & other refrigeration systems. ANY non-condensible gas is bad. Air, nitrogen, whatever. Any of that gets in the way of the heat-transfer that's supposed to be happening. A good vacuum pump gets it out, but it's real difficult to remove moisture. The reason you want to try to dry it first, is that a vacuum takes FOREVER to remove moisture. It might work if you leave the vacuum pump running at least 15 or 20 hours.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hatch &raquo;</TD></TR><TR><TD CLASS="quote">For a 115/208/230/460V compressor, acid eats the windings resulting in opens/shorts.</TD></TR></TABLE>Lot of commercial systems use a canned-motor compressor. That means the electric motor is actually INSIDE the pressure boundary. There's no shaft seals to leak, but the motor is immersed in the refrigerant. That's not the same for cars because the AC isn't driven by an electric motor.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eda6 hatch &raquo;</TD></TR><TR><TD CLASS="quote">It is possible to to make the moisture freeze when pulling a vacuum. Can't explain this one . I'll get specifics tomorrow.</TD></TR></TABLE>I'd explain but it would make your head explode.
(If the partial pressure of water goes below 0.0886 psia, the saturation temperature is below 32 degrees F.)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">-30 psi is impossible. It was -30 inches of mercury.
</TD></TR></TABLE>
yea, i wasn't sure. i just quickly glanced at the gauge he had and all i remember was it being at -30. i didn't remember what kind of measurement. well, at least i know now.

Anyways, using the blacklight we found a couple of droplets of uv dye coming from underneath the evaporator. So....i dunno, MAYBE, i'll buy another one and try again.