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ASEMaster35yrs
ASEMaster35yrs, Chevy Technician
Category: Chevy
Satisfied Customers: 2095
Experience:  ASE Certified since 1972,Master Auto tech,Heavy Truck Tech ,chev dealer tech
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Chevrolet tahoe: Ac not working.replaced head unit,comptressor,drier,orriface

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Ac not working.replaced head unit,comptressor,drier,orriface tube,condensor,both lines/schrader valves low pressure switch,evacked and hold/no leaks,oil and freon of course,high 140 low 35,electric 12 volts all over,relays under hood checked,clutch wont kick in to blow cold.97 tahoe 5.7-help!

Welcome to Justanswer ! my name is XXXXX XXXXX i will do my best to assist you with this problem

the compressor will never turn on ?

and if you pull out the compressor relay it has 4 terminals on it correct ?

Customer: replied 4 years ago.

2 on top just behind clutch 2 on back of .compressor

ok in the underhood fuse box is there an A/C compressor relay in there ?

# XXXXX in this picture

 

 

Customer: replied 4 years ago.

yes

ok pull out that relay and there should be 4 terminals

with the key ON do 2 out of the 4 terminals show 12 volts ?

Customer: replied 4 years ago.

fuse panel at dash and under hood all checked showing power including wires .when run direct current to switch on top of compressor it kicks in but not through system itself.

ok can you see if 2 terminals at the compressor relay show 12 volts with the key on ?
Customer: replied 4 years ago.

thats whats weird,showing power yet it wont kick in.

do 2 show 12 volts with the key on ?

if so with the engine running and the a/c ON does one of the other 2 terminals show a ground only when the a/c switch it turned on with the engine running ?

Customer: replied 4 years ago.

yes,i am telling u this info according to what i seen the mechanic do and what he told me.went thru all the chacks and balances and said all is proper must b the head unit.replaced with factory original yet still nothing.

we have to know this !

 

do 2 show 12 volts with the key on ?

if so with the engine running and the a/c ON does one of the other 2 terminals show a ground only when the a/c switch it turned on with the engine running ?

Customer: replied 4 years ago.

right after u had me check the relay box under hood a severe thunder storm broke out and i am delayed to physically go probe with my voltage testerl/car in driveway.sorry for the delay.typical fl. weather.

no problem
Customer: replied 4 years ago.

I AM BACK AND YES TWO SHOW POWEE AND ONE GROUND WITH TRUCK RINNIN AC ON

ok and that ground will only come on and off when you turn the a/c switch on and off ?

are you 100% sure ?

Customer: replied 4 years ago.

DIDNT TURN ON AND OFF LET ME CHECK

2 terminals should show 12 volts and ONE of the other 2 terminals should show a ground when the engine is running and the a/c is turned on
Customer: replied 4 years ago.

GOT THE SAME ON OR OFF THEN MY TESTER JUST DIED

ok so no ground turning on and off correct?

if so the computer is not telling the relay to turn on and then we need to see if the computer is being told to turn on the a/c

put the relay back in and with the engine running with the a/c on and one switch at a time unplug the high pressure switch and jump the 2 terminals in the connector and see if the compressor turns on if it doesn't plug that back in and try the same with the low switch then try the cycle switch see if any you jump will turn the compressor on

Customer: replied 4 years ago.

OK

let me know
Customer: replied 4 years ago.

NO CHANGE CLEANED A LITTLE PAG OIL OFF ONE CONNECTOR AND THE ONLY THING WAS LOW PRESSURE RAISED MY IDLE

lets see if any other experts have any ideas hang on

another expert will reply back to you

Customer: replied 4 years ago.

OKAY,ANY CHANCE THIS HAS OTHER RELAYS.SAW A FORUM WHERE GUY SAID SOME IN PASSENGER KICK PANEL AND WAS LOOSE AND WAS HIS PROBLEMK?

Hi, glad to be of help. First of all, you are low on freon. With compressor clutch engaged Add freon until your high side shows 200-225 psi. If your high side reading does not increase, your compressor is defective. How are you getting compressor clutch to engage? Are you connecting it direct? The ground is supplied through PCM. Check your connections there. With a scan tool find out if you are getting a request for AC clutch engagement. If you are not getting the request, the problem is most likely in the HVAC module. Here is a diagram:

graphic

ASEMaster35yrs, Chevy Technician
Category: Chevy
Satisfied Customers: 2095
Experience: ASE Certified since 1972,Master Auto tech,Heavy Truck Tech ,chev dealer tech
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