1991 Toyota Pickup Air Conditioning issues
 

I have a 1991 Toyota Pickup 4x4 22RE Standard Cab - 382,000 miles, just had the engine and transmission rebuilt.


I just had my AC recharged. It blows cold air, no problem. The Compressor seems to have no problems.


Here are the issues:


- When set to the lowest setting inside the cab, the fan does not engage (the fan behind the glove box). When set to the next highest and subsequent settings, the fan engages and blows cold air.


- After 20 min of running, I hear a click click sound (a similar sound like a light switch going on and off). It repeats itself over and over sometimes several times over a 2 - 3 min period. Feels like the compressor is going on and off because I can feel the change as I am driving with the engine.


- There is also a clunk type sound, sounds like a valve opening and closing. This happens sometimes, usually in the first few minutes after turning on.


I have isolated these sounds to inside the black plastic box, left side of the fan right behind the glove box.


I have attached a photo showing this box, it is the one to the left of the fan grill with the white writing on it.


Any ideas? I am thinking a switch issue (Blower Motor Switch? Compressor Cutoff Switch?) if you think it is one of these switches, where are they located? under the dashboard, I assume?

The clicking sound is most likely your cut-off relay. If it's clicking, most likely the relay itself is working fine. Check all the connections for corrosion.... actually, I'm not sure if your 22RE will have the cut off relay...

Check/clean the contacts on the switch for the blower motor for the low setting.

Cut-Off Relay and Blower Motor Switch
 

I assume I would find these under the dashboard. But, where? inside that black box in the photo I sent?


Under all circumstances, my AC works good. Just makes these sounds which give me some worry that something is about to go out. Never heard these sounds before.

According to this you don't have a cut off relay.
http://personal.utulsa.edu/~nathan-b.../2aircondi.pdf

Which means it could be the other relays.

When this sound is coming on/off does the AC behavior change? Maybe something just got in the blower/fan?

The AC behavior does not seem to change. Still blows the same cold air at the same level, but I can feel my engine hesitating very slightly like when the compressor starts and stops.


Think it could be the Compressor Cut-off Switch?

I checked the blower fan, behind the glove box. It spins in the medium and high range, but the low range it stays off. But, this is a separate issue.

Where in the heck is all the AC relays and switches located?


Thanks for the help so far. This is real good stuff.

Better to pick low-hanging fruits first. Better to check/test the simple things first. Better to replace IF, and only IF necessary, the less expensive things first.

I suggest you check your blower resistor AND your fan switch. As you describe above, something is obviously wrong with one of them.

IF you verify that absolutely nothing is wrong with the above, then move on to the more complex, more challenging, and potentially more expensive stuff.

Where is the Blower Resistor and Fan Switch? are these under the dashboard.


I figured out what that black box is I mentioned above. It is the Cooling Unit.

The relays/switches are on the upper right behind the glove box. Near the door hinge.

If your engine behavior is changing, then most likely your magnetic clutch is engaging and disengaging with the clicking, which means one of the relays is switching the clutch... in that case it can either be the relay or the wiring, or the control system which is mainly the amplifier/input signals. If the problem is intermittent, it's gonna be tough to find which part of the circuit is the issue.

Ok, I found the Blower Resistor and Fan Switch. Let me see if I can find the other items I mentioned above.


Believe me, your posts are helpful. Many thanks. Please if you think of anything else please post it here.

Since it is not intermittent, it sounds like it is likely one of the relays. My wiring appears all good and clean. I will take a look at this location. Thanks for telling me.

It's not abnormal for the compressor to cycle on/off every few minutes after it has things cooled down. If it didn't, the temperature of the evaporator would continue to drop and eventually get below 32 degrees. At that point the humidty of the air will freeze on it and ice it up, blocking the flow of air through it so you no longer get any cooling.

How often the compressor cycles is a function of outside temperature, the amount of refrigerant in the system, and the overall effiency of the AC system. R134 systems cycle less than R12 systems did, because R134 doesn't cool as well and has more difficulty getting down to freezing temperatures.

Ok, I found my Blower Motor Relay and Blower Motor Resistor. I plan on replacing these myself once I receive the parts.


Where is the Compressor Cutoff Switch? I would like to replace this one as well. Is it somewhere under my dashboard that is easily accessible?

I replaced my A/C-Heater Blower Relay, Blower Resistor, and Blower Switch. The hard part was trying to extract the Blower Switch, those little tiny plastic clips holding it in are very easy to break. I busted 2 of them despite being super gentle, plastic likely got more brittle over the decades. Luckily the other clips still hold the switch in place no problem. I tested my A/C and blower seems to run better now, noticeably better. Heck, it even works in the low setting! The ultimate test will be when I drive it to work this week. My blower resistor was corroded with green crust at its base. The work was not difficult just be careful not to break all those plastic parts and plan to get used to working in yoga positions!!!

Thanks will look into mine

Well, I finally drove my truck to work today. Turns out the AC issue I described at the start of this thread is still there. What else could it be? I already replaced the Blower Motor Relay, Blower Resistor, and Blower Switch.

Could the Expansion Valve inside the Cooling Unit be the problem? The "clunking" sound like a door being opened and closed is coming from inside the Cooling Unit (yes, I know where this is now).

found the problem!!!
 

My A/C was overpressured, plus my Blower Resistor was corroded. Discharged and recharged my A/C at the correct pressure and changed the stuff I mentioned earlier. Works great now!

Sweet! happy for you.