• If you currently own, previously owned or want to own an Avalanche, we welcome you to become a member today. Membership is FREE, register now!

Diagnosing AC Low and High Side Pressures Need help!!

senorv47

Full Member
Joined
Jul 31, 2014
Messages
29
2002 Avalanche, 1500, at ambient outside temperature of 87 Degrees and normal operating temperature at idle I have Low side Pressure of about 42 PSI and High Side of about 220 psi. AC on and compressor running I am getting cold air from the ducts.  After about 10 minutes Low side came up to 45 PSI and High side 225, compressor still running and ducts cool.  I got in the vehicle and revved the engine a bit and suddenly the Low Side went to 100 PSI and the High Side went to 110 PSI, compressor stopped running and warm air from the ducts.  What is wrong here, I am not sure
anybody have any ideas?  Thanks in advance
 
Take to a repair shop maybe?

Unless you get lucky and someone here knows a lot about A/C.

When you revved it did you stomp on it?
Might be a cutout for when you stomp on it...

Does it blow hot when you normally drive it?

The Pressures sound in range of where mine were when I put a gauge on it.

 
Thanks, I would take it to the repair shop if I had the crazy money they charge to repair anything.  Besides I do have mechanical skills and the tools to do it so why waste them.  Anyhow, no I did not stomp on it, just a couple of revs.  Normally it starts out cold then after about 20 minutes it goes warm.  Yeah, I was thinking it started out in the correct range but then something changed and the low pressure side went high which I believe changes the state of low pressure switch which cuts off the compressor.  Just have to figure out what, could be the low pressure switch is bad but not sure.
Someone out there has the answer.  Thanks for responding.
 
I think the condenser coil is pretty dirty or someone has added to much refrigerant, that is a high head pressure  Probably opening the relief valve because of increasing the compressor revs.
 
Also put thermometer in the center main dash vent.

Keep eye on coldest air temp it can do.

Pressures equalize because compressor kicks off.

It will kick off for low pressure on low side and high pressure on high side.

When you rev too quickly or over certain RPM I think they cut off to prevent overspeed but should hang in there  up to 4000 RPM easily.

Slowly rev it up and hold 2200 rpm and watch pressures ... - Have someone elese listen for Compressor clutch clicking too so you can know the pressure it kicks off... would be high point on gage when it suddenly drops.

IT could be overcharged as stated above - but someone had to add soem as that does not just happen on its own. so if no one worked on it I doubt over charge  unless thee are Re-charge Angels.

Could be the orifice tube is clogged which would cause high pressure to build quickly as rpm increases... to change you have to evacuate and pull it out and if you change that replace dryer as too.

What work was doen to it recently if any?
 
Thanks, I will do that this afternoon, I did plan on checking the Freon level this afternoon,  and I will review the gauge reading again with someone in the driver seat slowly revving it up.  Yesterday I was by myself and did the revving myself.  I noticed the temp change immediately but did not notice at what rev level.  When I when around to check the gauges the low side went up from 45 to 100 PSI and the high side had drop from 225 to 110 PSI and the compressor had stopped running.  The Freon level was low last Summer and I used a refill kit to bring it up. it is possible that I misread the gauge and overfilled it. So it is probably my fault.  Thanks for your input.  I will report back with my findings this afternoon.

ygmn said:
Also put thermometer in the center main dash vent.

Keep eye on coldest air temp it can do.

Pressures equalize because compressor kicks off.

It will kick off for low pressure on low side and high pressure on high side.

When you rev too quickly or over certain RPM I think they cut off to prevent overspeed but should hang in there  up to 4000 RPM easily.

Slowly rev it up and hold 2200 rpm and watch pressures ... - Have someone elese listen for Compressor clutch clicking too so you can know the pressure it kicks off... would be high point on gage when it suddenly drops.

IT could be overcharged as stated above - but someone had to add soem as that does not just happen on its own. so if no one worked on it I doubt over charge  unless thee are Re-charge Angels.

Could be the orifice tube is clogged which would cause high pressure to build quickly as rpm increases... to change you have to evacuate and pull it out and if you change that replace dryer as too.

What work was doen to it recently if any?
 
When you added last year was it totally out? If so and you added more in then you will have air in the system and that could cause your problem also.
 
LornesAV said:
When you added last year was it totally out? If so and you added more in then you will have air in the system and that could cause your problem also.

Good point, when I pulled the gauges of yesterday the high side hose came off no problem but when I pulled the low side it was like the valve was stuck and only air (not Freon) was coming out.  I tired to close the valve (put cap on it, but air was not cold) but it did not work so I put the gauge back on and remove it and it stopped so maybe I have air in the system?  Don't know how it got there because I have never disconnected and parts of the system.

By the way all I was suppose to post more psi readings today but got to busy working on something else so going to try for tomorrow.  Everyone have a  great Memorial day weekend.  I live at the beach so my weekend is always good.  Thanks for all the great input!!
 
LornesAV said:
When you added last year was it totally out? If so and you added more in then you will have air in the system and that could cause your problem also.

No wasn't totally out, it was the beginning of my current issues.  It was doing the same thing it is doing now, but as the outside temp dropped they better
it worked of the outdoor temp is 70 it will cool all day but when the temp is above 80 it goes to hell.
 
Might be low again and when you rev it up the low side pressure drops too much so it kicks off....

If it is low again you have leak and should get it repaired.
 
Thanks for the response.  Yes could be I intended putting the gauges back on the last few days but had some other issues so I had not gotten back to it.  Hopefully
I can rerun tests today and post my findings.


ygmn said:
Might be low again and when you rev it up the low side pressure drops too much so it kicks off....

If it is low again you have leak and should get it repaired.
 
Last year when my AC was not working right I found a rebuild kit... It contained all of the o-rings and the shrader valves you need to do the whole system.

Next time you do fill it up make sure you put some dye into the system so you can track any leaks.

Been told that with the dye it becomes real obvious where the leak is pretty quick.

Somethings are worth the money to let someone else do and one of those is AC diagnostics... You can always have them evac the system and install the compressor yourself if that is the issue...  and most of the other parts...

If I had the time I would probably replace every o-ring in my system and consider the compressor too. But my truck is an '03 with 260k miles on it so it could very well be worn out.

Rodney
 
Thanks for the response, I will look into that if it comes to that.

redheadedrod said:
Last year when my AC was not working right I found a rebuild kit... It contained all of the o-rings and the shrader valves you need to do the whole system.

Next time you do fill it up make sure you put some dye into the system so you can track any leaks.

Been told that with the dye it becomes real obvious where the leak is pretty quick.

Somethings are worth the money to let someone else do and one of those is AC diagnostics... You can always have them evac the system and install the compressor yourself if that is the issue...  and most of the other parts...

If I had the time I would probably replace every o-ring in my system and consider the compressor too. But my truck is an '03 with 260k miles on it so it could very well be worn out.

Rodney
 
UPDATE: It is looking like you were right, turning out like I did not understand Voodoo AC works and reading the gauges wrong.  When the gauges are reading 100 psi is because the compressor is not running, once fill is applied and compressor starts running and it starts dropping,  you can read the true reading on of Freon level.  My initial readings on the low side of 45 and above with the compressor running should actually have been around 35 psi which accounted for the AC not being as cool as it could be.  What threw me off was when it jumped to 100 psi, which I could not understand in my pea brain.  Not sure that I have a leak but will drop some leak sealer in it just in case.  Thanks all!!


ygmn said:
Might be low again and when you rev it up the low side pressure drops too much so it kicks off....

If it is low again you have leak and should get it repaired.
 
Back
Top