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#61 ken1mod

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Posted 08 October 2010 - 11:21 AM

usually, electric fans turn on with the a/c even on a cold engine. If the truck cools ok, leave it alone.
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#62 USMdude

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Posted 08 October 2010 - 12:25 PM

Here's a question for you guys...on my Grand Am I notice the A/C works beautifully (ice cold even in 105 TX summer), but only after the engine is at regular, warmed-up temperature. The fans do come on when the engine is cold when I turn on the A/C, which is correct, but they turn slowly, like a slow-speed. Once the engine is hot, the fans run full-blast and the A/C works sooooooooo much better.

There are no obstructions I see in the rad/condenser...is this pretty normal?


This sounds perfectly normal. For the coolant fan.......... As long as the accumulator has condensation on it and the engine is not over heating, leave it alone.

Jbo

#63 ken1mod

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Posted 08 October 2010 - 07:42 PM

Gentlemen,

A good omen is condensation on the accumulator. Remember this though, when the weather starts to dry out like this time of the year, there may not be enough moisture in the air to condense on the accumulator. It still should be cold though, about 40 degrees or so.

Many things are better when wet but a non sweaty but cold accumulator is perfectly healthy.

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#64 blacksierra01

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Posted 08 October 2010 - 08:47 PM

hi, got an a/c related problem. a/c works fine when its not insanely humid and while on the highway, it seems to lose its cool in traffic or around town, and once its gone it wont come back until it cools of outside like at night. the condenser isnt plugged, could it just be low on referigerant or is it somthing else?
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#65 MerriAnn

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Posted 18 October 2010 - 05:02 PM

the Air Conditioning does not work. Compressor does not kick on and off. When temp. dial is turned torwards hot or warm, them compressor will start kicking off and on., like it should. Bypassed low pressure switch, compressor still won't kick on and off when the A/C is on. Checked connections to compressor, it has the right voltage. Freeon was checked and it's full. Once in a great while, it will work for a short period of time, like 3 to 5 minutes and then the compressor quits kicking in and out. Checked condensor and it is free of debris. I put a new compressor belt on. The heat works great. Accuator door is working properly. This truck is a 2000 Chevy Silverado 2500 4x4 with 6.0 liter, Automatic trans. I tried posting this in the general forum, but, have not gotten any answers?

#66 roket10r

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Posted 20 October 2010 - 09:13 AM

Gentlemen,

By trade I am an air conditioning engineer and i have some good advice for the people on this forum.

Many of us check the temperatures of our a/c units once in a while. I love my IR thermometer where you just point the device at the a/c outlet and read the temp. Great fun.\\We also may notice that the temp is not as cold now as it was in early june before the humidity went up.

This is NORMAL. Humidity is the same as heat to your a/c. I would see 40 degree air in june and now the temp is in the 50s.

Pressures? Who cares. As long as the unit is cooling and the accumulator is cold to the touch, it is working properly and charged correctly. Adding more refrigerant at this point will cause the unit to run constantly (not cycle as it is supposed to) and put out warmer air. Pressures can be important to diagnose major problems but this is rare.

A dirty leaf covered condenser will cause high high side pressures but you can look at the darn thing and see that it is dirty. I don't think I have ever hooked up the high side gauge unless I was trying to impress my wife. Refrigeration happens in the low side of the system. If the unit is cooling the car and the accumulator cold, it is properly charged. You actually do not need gauges to properly charge a healthy system that is just a bit low on refrigerant.

A properly charged system will cycle on the accumulator pressure switch every minute or so. It does this to keep from chilling the evaporator below 32 degrees which would freeze it into a chunk of ice blocking airflow.

So, if your unit is not cooling the vehicle well and you think it may be low on refrigerant, start the engine, have someone hold about 1200 rpm with the blower on high. Open the hood and give things a couple of minutes to stabilize.

Put your hand on the accumulator. If it is not cold, add maybe a half can of refrigerant slowly. The unit is perfectly charged when the accumulator is cold and the unit cycles about every minute or so. The cycle time varies with conditions but it should cycle. If it does not cycle ever, even at a lower blower speed, the unit is probably overcharged. These units are not charge critical and will work great plus or minus a half pound or so of the correct amount and they all leak slightly from hoses and particularly the shaft seal of the compressor. This is why they are designed to not be charge critical.

I hope this info is useful to anyone having problems.

Ken


What would cause the A/C unit to quit working and start blowing hot air w/o any changes to control panel. I've had this happen several times and the only way to "reset" the system is turn the truck off and re-start the engine. Has anyone else had or having this problem?
As soon as the motor is re-started the A/C is back cold and works fine. This has happened while driving on the road and as soon as I'm able to get clear of traffic, just put in neutral and turn the key off and re-crank...problem solved until the next time. Any help with this ?

Edited by roket10r, 20 October 2010 - 09:27 AM.


#67 spurshot

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Posted 04 December 2010 - 12:05 AM

I'm not of Ken's experience and education on A/C, but I've bought all the equipment and done my own and some friends for a few yrs now. The biggest reason for no A/C function or intermittant function I've seen has been an over tolerance gap of the clutch. The test for this is simple. Just turn on the engine and A/C and tap the clutch with a hammer or such and see if it engages. If it does, it's likely the gap is too large.

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#68 dsch

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Posted 08 December 2010 - 09:36 PM

One other rule of thumb I use is a 20 degree celsius drop in temperature from the inlet to the outlet of the condensor.


And clean cab air filters if you have them.

#69 teknition

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Posted 22 January 2011 - 01:03 AM

Hello guys, this seems like a good place to ask about my ac question.

I have a 95 Sierra with nice working cold ac, the compressor cycles on and off just fine and condinsates great.

My question however is, any time i start up the truck the compressor will cycle on and off (normally) for a while. but after i get to town i check the "cold line" it is out side temp or normal temp for it being off.

and that is my question. When I am not using the ac , it cycles as if it were on and will get cold and drip, but after a run to town it seems as if it never did. but when i start it up again and let it idle , it will cycle and get cold.


The manufacturer designed this into the HVAC system for 2 reasons:
1) To help keep the compressor shaft seal from drying out resulting in loss of refrigerant.
2) One of the things an a/c system does is remove humidity from the cab. Cycling the a/c on for a short duration on startup aids in defrosting your windshield in the winter.

Brad

EDITED TO ADD "PJ is right, I finally noticed about a month ago that when i turn the dial past "floor" towards defrost/floor or just plain defrost, the compressor will kick on. but when i turn it back it goes off. I am doubting that is a standard feature."

The compressor will cycle whenever the zone control is in any position that has anything to do with defrost.

Edited by teknition, 22 January 2011 - 01:08 AM.


#70 teknition

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Posted 22 January 2011 - 01:34 AM

Here's a question for you guys...on my Grand Am I notice the A/C works beautifully (ice cold even in 105 TX summer), but only after the engine is at regular, warmed-up temperature. The fans do come on when the engine is cold when I turn on the A/C, which is correct, but they turn slowly, like a slow-speed. Once the engine is hot, the fans run full-blast and the A/C works sooooooooo much better.

There are no obstructions I see in the rad/condenser...is this pretty normal?


Your Grand Am is equipped with variable speed fans, running at a slow speed when the engine is cold and the high side A/C pressures are low is normal. As engine compartment temperatures rise and/or high side A/C pressure rise the fans will turn faster to get rid of the heat.

As for working better after the engine is hot, you have to remember that there is a tremendous strain on the A/C when first starting. When you first climb into your car, your interior is very hot, the hot air is blowing past the evaporator core and the core is absorbing as much heat as it can, but can only absorb so much, the remaining heat in the air flowing past the core is redistributed into the car. The a/c system works by removing heat form the interior and releasing it outside the vehicle, it doesnt make cold and distribute it to the interior. This is accomplished by pressure differential between the high and low sides, and at start up the compressor has to have some time to make that pressure differential.

One of the best things you can do to help the A/C system cool the interior off quickly on startup is to roll your windows down for a minute and let the heat that has accumulated out of the interior.

Brad

#71 teknition

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Posted 22 January 2011 - 01:47 AM

hi, got an a/c related problem. a/c works fine when its not insanely humid and while on the highway, it seems to lose its cool in traffic or around town, and once its gone it wont come back until it cools of outside like at night. the condenser isnt plugged, could it just be low on referigerant or is it somthing else?


Could be low on refrigerant... Could also be an air flow problem at the condensor. Does it get cold again if you go back out on the highway? If it doesnt, I would say low on refrigerant. If it does, I would look for lack of air flow thru the condensor. May not be a plugged condensor, could be a missing fan shroud, loose fan belt, damaged fan blade, or a defective fan clutch. You can verify this by running the a/c on the highway to get it cold, then bring it back home and let it run in the driveway and go warm. Have someone sit in the car with their hand over the vent and another guy to keep a garden hose spraying water on the condensor. If it goes cold when the water is being sprayed on the condensor, you have an air flow problem and arent getting rid of the heat at the condensor.

Brad

#72 arzinet

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Posted 07 February 2011 - 08:28 PM

I don't have an A/C problem with my truck, but do have an A/C question that has been bugging me for a long time.

On my '07 Suburban, the A/C compressor will not engage at temperatures below 3 or 4 degrees Celcius (around 37 F). It says so right in the owner's manual, but doesn't explain why. I assume it's because the compressor can't deal with the condensation/evaporation at below-freezing temperatures?

If that's the case, is it the same for all other automotive A/C systems, or do some makes have a way around this problem? I'm curious, because the A/C in other vehicles I've owned (VW, Honda, Nissan) didn't work in below freezing temperatures either, yet the owner's manuals never come right out and say it like GM does.

It's not a big deal, but I find it interesting that 95% of drivers assume their A/C works just as well in the winter as it does in the summer (and up here, winter means well below freezing). Not that we need it for cooling of course, but people think it's useful for defrosting windows. Not in my experience, but people still swear by it.

Any light that a real A/C engineer could shed on this for me would be much appreciated. :dunno:

#73 teknition

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Posted 12 February 2011 - 12:36 AM

I don't have an A/C problem with my truck, but do have an A/C question that has been bugging me for a long time.

On my '07 Suburban, the A/C compressor will not engage at temperatures below 3 or 4 degrees Celcius (around 37 F). It says so right in the owner's manual, but doesn't explain why. I assume it's because the compressor can't deal with the condensation/evaporation at below-freezing temperatures?

If that's the case, is it the same for all other automotive A/C systems, or do some makes have a way around this problem? I'm curious, because the A/C in other vehicles I've owned (VW, Honda, Nissan) didn't work in below freezing temperatures either, yet the owner's manuals never come right out and say it like GM does.

It's not a big deal, but I find it interesting that 95% of drivers assume their A/C works just as well in the winter as it does in the summer (and up here, winter means well below freezing). Not that we need it for cooling of course, but people think it's useful for defrosting windows. Not in my experience, but people still swear by it.

Any light that a real A/C engineer could shed on this for me would be much appreciated. :lol:



Im not an a/c engineer but have been a licenced heavy duty and automotive tech for the last 20 years. I have worked on a/c systems since I started my apprenticeship so I guess I will call myself qualified.

First off, a compressor doesn't deal with moisture, all it does is compress a gaseous refrigerant so that when it hits the condensor, the gaseous refrigerant is cooled by the condensor can change the state of that gas to a liquid. If you have moisture inside compressor you have a big problem. The only thing that should be flowing thru the inside of the a/c system is refrigerant and some oil.

The part of the a/c system that deals with the moisture is the evaporator core (inside your vehicle, in the heater box). It works the same as having an ice cold beer in the summer, the moisture in the air condenses on it and runs down (the glass) the evaporator core to be expelled via the heater box drain. Thats why you see water dripping out under your vehicle on hot humid days.

When I work on an a/c system in the summer, I'm happy if the vent temp gets down to 40 degrees F. Some will go a bit lower maybe 34-36 degrees. Vent temp is highly dependant on ambient air them outside the vehicle. You dont want the temp below that. A frozen evaporator core= fins covered in ice= no air flow= no cooling. If your 'Burban will get 37F out of the vents you should be one happy guy, you should be able to scrape the frost off the inside of your windshield with your nipples.

Remember, the a/c is designed to take the MOISTURE out of the air in the car that causes fogging/frost. When you expell moist air via your breath in below freezing themperatures, it isn't MOISTURE long enough to hit the windshield. As well, the frost on your windshield isn't moisture until it gets above freezing. Therefore the a/c cycling isnt going to do any good.

On older vehicles without an ambient air temp sensor, I dont see anything that could stop the a/c clutch from cycling, so they may well be cycling anyway, but the low side pressure would likely be too low to close the low side pressure switch and allow the clutch to engage. I havent charged many a/c systems outside in below freezing temps so never bothered to actually check that theory out.

Once the engine compartment temp comes up enough to allow the a/c compresor clutch to engage and cycle the compressor, the heater is starting to put out some heat and changing that frost on the window to moisture. That is when you want the a/c evaporator core to start to capture some of that moisture and get rid of it via the drain.

Hopefully that answers your questions, if not, ask away, I will still be here even though it is *all freezing cold out :)

Brad

#74 arzinet

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Posted 12 February 2011 - 03:39 PM

Thanks for your explanation!

So if I understand you correctly, the compressor doesn't care what the outside temperature is. The evaporator does, but since it's located in the heater box it shouldn't freeze in the winter with the heat cranked up and the A/C on (like you would in defrost mode).

That makes sense, so I'm wondering why GM has prevented the A/C from cycling on at low temperatures. Maybe it's as simple as the condensation from the evaporator freezing up and plugging the drain hose somewhere downstream of the heater box?

#75 dsch

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Posted 13 February 2011 - 01:09 PM

Thanks for your explanation!

So if I understand you correctly, the compressor doesn't care what the outside temperature is. The evaporator does, but since it's located in the heater box it shouldn't freeze in the winter with the heat cranked up and the A/C on (like you would in defrost mode).

That makes sense, so I'm wondering why GM has prevented the A/C from cycling on at low temperatures. Maybe it's as simple as the condensation from the evaporator freezing up and plugging the drain hose somewhere downstream of the heater box?


At a cold enough temperature teh compressor could start to compress liquid refrigerant, which since a liquid is non comressable is not good for the compressor




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