NUckINg FuTS

Last summer I was replacing the old R12 freon w/ 134a. When I tried hooking up the 134a my clutch would not engage. So far I've replaced the in dash electronic control, both switches on the high side of the A/C, and today a mechanic professionally evacuated and refilled the system with 134a. A/C fuse is good. Tried jumping the low side cycle switch, nothing. Only other thing I could think of is the electronic blower control module. I don't want to blow $140 on the module just to find out that that wasn't the problem. What else can I chech out or is there a way to check the blower module? Help, it's starting to get real hot over here.

vert2go89

the air gap in your ac clutch is to much and it wont engage or the cycling switch is bad or the clutch feild coil is bad.i would try adjusting the cycling switch first.there should be a screw in center of switch that you can turn and see if then clutch engages.

VetteNoob

Hey, I had the same problem after replacing almost everything on the AC system. It turned out to be a bad ground on the blower and the blower control module was toast. Cost me $280 to find all that out because I took it to a Vette shop to have them fix it. I got tired of throwing money at parts to chase the problem.

My $.02 blower module. :rolleyes: :mad

C4TOMCAT

if the blower is working thru the a/c controls, and the copressor does not engage, first jump out the terminals of the low pressure switch located either on the silver can accumulator or on the suction line leaving the evaporator by the firewall. use a small piece of wire and jump the terminals. then, turn the key to on, turn on the a/c and set temp to lowest and you should hear the clutch pull in. if not, tap it lightly with a small soft piece of wood and if it pulls into the coil then it may have too much clearance due to wear. you can just change the clutch if you work with tools ok. if the clutch does not pull in, check for 12 volts on the terminals going to the compressor coil. if 12 volts is there at the terminals, measure the ohm resistance of the coil with a multi meter. my coil on the 94 is 3.7 to 4.? ohms on a simpson 260 meter. digital would give slightly different.

the coil could be bad, so if you have to change the coil, change the clutch also because when the distance increases due to wear, you get the coil trying to pull in and it cant so it overheats and burns up. hope this gives you some guidelines. good luck.

NUckINg FuTS

I know the compressor/clutch is ok. If I connect a power and ground directly from the battery to the compressor the clutch will engage. Now if the blower controle module is bad wouldn't the blower motor and/or the heater not work at all?

The Dingo

Watching this thread too cause I have the same problem... :yesnod:

XtremeVette

yep me to.... C4Tomcat is also helping me out....

hopefully we will all be cool very soon!

:cool:

VetteNoob

Correct. If the module is out, then the blower will not blow at all. Did you check to make sure you are getting power at the compressor plug? You can put a volt meter at the cycle switch to make sure it is getting power too. Did you check to make sure you have enough 134a in the system?

C4TOMCAT

the a/c clutch relay is PCM controlled to delay a/c clutch engagement after the a/c is turned "on" to allow pcm to set idle rpm before the clutch engages. PCM engages A/C cltuch any time a/c has been requested unless ANY OF the following conditions exist
high coolant temperature
wide open throttle
low A/C system pressure
high engine rpm
high a/c system pressure
high oil temp.
when the a/c is placed in the a/c mode, 12 volt signal is sent to the PCM the PCM grounds CKT459 to energize the A/C relay. if the A/C refrigerant psi is greater than 429 psi or lower than 0 psi the a/c clutch will not engage
dtc 66 & 67 will be set if the a/c sensors signal wire becomes open, grounded, shorted to voltage then dtc 66 is set. if the a/c clutch engages and no pressure change is detected, dtc 67 is set.
whe a request for a/c has been detected by the pcm, the pcm will ground the a/c slutch relay drive circuit and the relay contacts will close, and current will flow thrugh the relay to the a/c compressor clutch. also, the pcm will tur on the cooling fans unless the vehicle speed is to high.

more to come. give me feed back on what you'v done.

C4TOMCAT

note all: the PCM will not activate the a/c clutch with a stored DTC. Make sure they are cleared.
relays are located on the right front wheel housing.
vin p with c60 and manual the a/c relay is the second one in reading left to right
vin p with c60 and auto trans, it is the first relay reading left to right
vin p with c68, manual it is the second reading left to right
vinp with c68 and auto....you lucky dogs, its the only relay on there.


[Modified by C4TOMCAT, 2:40 PM 6/23/2002]

VetteNoob

He has an 86 vette. I dont think our AC systems are controlled by the ECM.

C4TOMCAT

ok, did you do the a/c clutch test with the key on, a/c turned to coldest, and see if the clutch engaged. if not, find the relay and check it out for operation. you might also put the voltmeter on the clutch plug to see if you have 12 volts there. that will also tell you if the relay is energized. if no voltage, go to the relay. I cannot tell what the relays are but alot of them are the same relay, might try swaping one. check the part numbers on them as some are relays for the blower high and low and they may be the same for the clutch. don't forget to check ALL THE FUSES.

NUckINg FuTS

Where can I find the A/C relay? I didn't hook upa volt meter but did hook up a test light. It looks as if one of the terimals on the clutch plug is getting power while the other one is getting neither power or ground? I'll look into it more later. Thanks for the help so far.

C4TOMCAT

relays are located on the right front wheel housing.
vin p with c60 and manual the a/c relay is the second one in reading left to right
vin p with c60 and auto trans, it is the first relay reading left to right
vin p with c68, manual it is the second reading left to right
vinp with c68 and auto....you lucky dogs, its the only relay on there.

this is for my 94 so use it as a referance to find yours.

SunCr

No relay, just the module which supplies a ground for the clutch when it receives a signal from the dash assembly. Since the assembly is new, it should be ok, but if the problem started when you replaced the assembly, check the connector or if you still have it, you may want to try the old assembly. In order for the signal to be sent, the cycling switch (on the evaporator) and the high pressure cutout switch (on the high pressure or small line to the evaporator) have to be closed. You can check both by disconnecting and jumping the harness connector with a paper clip or checking the continuity of the switch with a DVM. If the high pressure switch is open, replace it. If the cycling switch is open, the charge is lost or the switch is bad. The ECM circuit, which is a 6 to 7 volt signal from the dash assembly to the ECM, has to be completed as well as the blower motor circuit (an open in the blower motor is the same as "off" to the dash assembly). Verify the module ground which is shared with the blower motor. Since your blower motor works, it's probably good, but you can trace the black wire from the blower motor up to it's splice with the module and inspect the splice. The clutch circuit is ignition voltage from the a/c fuse through the clutch coil and back to the module). To verify the circuit trace the wire you don't have voltage on (should be green) to the module and disconnect it. Grounding this wire should engage the clutch with the ignition on. If not, the wire is open (since you can jump the clutch with battery power, you all ready know the clutch coil is good). Finally, verify power to the module and that it is getting the clutch signal from the dash assembly. The module is powered through a fusible link and you should have 12 volts or battery voltage on the red wire to the module. Since your blower motor is working, this circuit should be ok. The clutch signal (with all of the aforementioned circuits completed) is 6 to 10 volts on the green yellow wire at the module. If you have the signal, but no clutch, the module is bad. If you don't have the signal, it's in the wiring to and from the assembly or the assembly. If the module is bad, check the diode in the clutch connector. If it's bad, replace it. Otherwise you could fry a new module. Hope this helps.

unixadmin

last week I needed to get my ac working due to this heat, and my 1984 a/c clutch wouldnt engage, it wouldnt even click on and off like the system normally does when its empty, I knew i needed to charge it because the butcher that did my engine rebuild purged the ac system and I was planning on at least charging the system. Well, you cant charge the system without the compressor running to suck in the freon stuff.

after checking fuses and trying to figure out why there was no voltage going to the compressor I was hot and desperate, I ran 10amp fused switch directly from the battery to the green wire on the compressor, this engaged the compressor clutch and caused the compressor to spin! so I charged the system using an r12 ->134a schrader adapter screw on thingy, cost me almost 20.00, three cans of 134a and a 6oz can of oil charge.

Now the system is just rigged up as a temp soution, I have to manually push an extra switch to turn on the compressor bypassing the old hosed 84 wiring etc. but I was able to get it to work, and now I can drive in comfort. Its possible to check your a/c clutch operation by using a jumper wire, and you can even use the same hack to cool things down until you figure out where the problem lies. [IMG][/IMG]