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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2000 Suburban and my a/c seemed to be working fine- until

Customer Question

2000 Suburban and my a/c seemed to be working fine- until about last week i noticed on full cold it seems to cycle between cold/warm constantly. No idea whats wrong and i have no codes or lights or anything. any help would be great! thanks
Submitted: 5 months ago.
Category: Chevy
Expert:  david craig replied 5 months ago.

Hi Im David, usually when the ac cycles like that its an indication of low refrigerant levels. Have your refrigerant level checked. when was the last time you had the ac serviced?

Customer: replied 5 months ago.
let me give you some other details maybe this will help- at highway speeds the air is colder. when I'm sitting in traffic its definitely warmer on the same settings.
Expert:  david craig replied 5 months ago.

ok. when you turn the ac on, does the cooling fan kick on?

Customer: replied 5 months ago.
maybe I'm missing it isn't there only one fan?
Expert:  david craig replied 5 months ago.

there should be an electric fan snug up against the radiator

Customer: replied 5 months ago.
hmmm. like behind the shroud for the huge radiator fan? I honestly though that fan did both.
Expert:  david craig replied 5 months ago.

usually there is 2 fans. one for the engine temp to keep it cool and one for the ac to keep air flowing through the condenser to keep the ac cool at idle

Expert:  david craig replied 5 months ago.

it should look like this

Customer: replied 5 months ago.
ok yes its turning on
Expert:  david craig replied 5 months ago.

ok good, then next check the front of the condenser for blockage of debri and dirt.

Customer: replied 5 months ago.
if its in front of the radiator then no there is no problem.
Expert:  david craig replied 5 months ago.

yes that would be it. ok. my advice to you would be to have the refrigerant level checked. that is a must before going forward.

Customer: replied 5 months ago.
as in with gauges? if so- what am i looking for?
Expert:  david craig replied 5 months ago.

yes manifold gauges...

Customer: replied 5 months ago.
i can rent them. so what am i looking for?
Expert:  david craig replied 5 months ago.

what you will be looking for, with the car shutoff. low pressure should read about half of the ambient air temp i.e. if it 80 degrees out the low pressure gauge should read approxiamately 40. and the high pressure should read approximately double the temp i.e. 160

Expert:  david craig replied 5 months ago.

that would indicate a good charge

Expert:  david craig replied 5 months ago.

then start the car put the ac on max and watch the gauges. low pressure should drop to around 20 then kick back on and go up to 40, then then the high side should go up to 250-300 then kick back on and drop back to 160

Customer: replied 5 months ago.
ok so here is what i have found- sitting at idle with vehicle on, max ac, the temperature in the middle vent is 70 degrees. when i rev and hold rpms at 2,000 (or more) with max ac the vent temperature is stead 62 degrees. what does this mean?
Expert:  david craig replied 5 months ago.

that the radiator fan is turning faster and is helping cool down the condenser as a supplement to the condenser fan.

Customer: replied 5 months ago.
ya lets get back to that- there is no other fan, only a radiator fan. regardless i have the gauges on it now- at 2,000 rpms low side stays at 62ish and high side is nearly 330- and they stay there. when i let off gas and let it idle low side is 60ish and high side goes down to 250. so what is the problem here?
Expert:  david craig replied 5 months ago.

just let it idle dont worry about revving it. then let me know what the gauges go

Expert:  david craig replied 5 months ago.

do you have the valves open at the service port connections

Customer: replied 5 months ago.
valves are open. and i posted idle readings above
Expert:  david craig replied 5 months ago.

my bad. how hot is it where you are?

Customer: replied 5 months ago.
todal 92 degreesF
Expert:  david craig replied 5 months ago.

is the compressor cycling?

Customer: replied 5 months ago.
its on constantly it seems
Expert:  david craig replied 5 months ago.

ok. gimme a minute and let me look at my manual

Expert:  david craig replied 5 months ago.

what size engine is in that thing?

Customer: replied 5 months ago.
6.0L
Expert:  david craig replied 5 months ago.

ok. now, turn the ac off of max ac and set to regular. tell me if it cycles then.

Customer: replied 5 months ago.
no on any settings it is not cycling off at all
Expert:  david craig replied 5 months ago.

ok, thats ok. just sitting with no airflow across the condenser im not surprised its not cycling

Expert:  david craig replied 5 months ago.

if you shut the truck off anf let the pressures bleed down, what readings are you getting? let me know. itll take a while for the pressures to bleed all the way off.

Customer: replied 5 months ago.
why isn't the compressor cycling? my wife is about to drive it again so i can't look at the the pressure now.
Expert:  david craig replied 5 months ago.

because of the outside temp and the fact that its sitting idle with no airflow across the condenser, the compressor will run constantly trying to keep the passenger compartment cool.

Expert:  david craig replied 5 months ago.

do you still need assistance?

Customer: replied 5 months ago.
not sure. sure enough there hasn't been any issues the last 24 hours. regardless, so like i said earlier there is no "Ac fan" that you told me was down in there. So, where is this second fan?
Expert:  david craig replied 5 months ago.

some dont have the extra electric fan ,apparently yours is one of them. I know that people install them as a supplement to the radiator fan in hot wether climates though

Expert:  david craig replied 5 months ago.

if you did have one it would be mounted snug up against the radiator or in front of the condenser

Expert:  david craig replied 5 months ago.

any progress?

Customer: replied 5 months ago.
ok so how does this work then? If i don't have a fan- how does the ac get the right amount of cooling with no fan?
Expert:  david craig replied 5 months ago.

well the radiator fan is supposed to be sufficient enough to coll the radiator and the condenser while sitting at idle

Expert:  david craig replied 5 months ago.

A fan clutch is as reliable as any other component on a vehicle, yet sometimes they fail. A common symptom of fan clutch failure is overheating at idle or in heavy traffic. Bad fan clutches can also cause poor performance of the car's air conditioning system because the fan also cools the air conditioner's condenser, which is directly in front of the radiator. A fan clutch can also fail in a stuck on position where engine power is lost even when the fan is not necessary. This type of failure can also decrease fuel economy.

Expert:  david craig replied 5 months ago.

do you still need assistance?

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