2001 Tundra, AC warm, pressure at 75psi, no leaks, comp clutch engages. What’s next?

Hi guys. My first time posting here and I’m working on my dad’s 2001 4.7L Tundra that blows warm air. The compressor clutch is responding to the AC switch and I measured the low side at 75psi (using a refill kit gauge), which is very high, correct?

After some reading here, I just realized I can check the high side as well. What tool do I need to do that, considering the refill kit’s hose only fits the low side? What should the nominal reading be for each side? Is it even necessary to check the high side or should I be looking elsewhere?

I don’t know much about AC systems, but from what I’ve seen on general YouTube videos, there’s a valve in the cab somewhere before the evaporator that opens the low side return. Is it possible this valve is stuck closed and I’m just reading the static pressure in the line from the valve to the compressor low side port? What is my next logical troubleshooting point?

Lastly, can anyone point me to a exploded view of the system or the factory service manual? Thanks in advance for any advice you guys can offer!

 

I'm not an AC expert, so I'm no help there.. The only thing I can suggest to check is the blend door that's actuated by the hot/cold knob on the HVAC bezel.

The connecting rod from the knob goes to a valve pictured below. Denoted by the blue arrow. (Below is V6 engine bay. V8 blend valve should be in similar location.)


Turn the knob all the way to HOT, and take a picture of the valve. Turn it all the way to cold, and take a picture of it.

Post them here. If it's not moving you'll have to pull the HVAC bezel out which is easy, and see what's not connected/broken.

This is the only thing I can offer as help. Perhaps others may know more. @Professional Hand Model @FrenchToasty @Darkness @bmf4069

 

I'm not good on AC stuff. There are a few things on cars that I consider black magic. Window tint, properly installing gears, transmission work, and AC work.

 

Wait so if the knob for the AC is completely missing, the AC will not function? Because the knob is broken and not in position. I used pliers to rotate the square shaft to the cold position. Thank you for the reply.

 

The AC will still function, but if you turn the knob, and that valve in the engine bay doesn't open with heat, or close with cold then you'll constantly be blowing hot air if it's stuck open. The AC isn't stout enough to knock the heater core heat out of the air.

Also, I have a set of these cheap knobs because one of mine broke too.

AC Heater Climate Control Knob Set of 3-55905-0C010, 559050C010-2000, 2001, 2002, 2003, 2004, 2005 & 2006 Toyota Tundra AC Knobs - Air Conditioner HVAC Blower Fan Temperature Switch

Link

 

Wow my Dad is gonna be so happy if this is the problem. Thank you so much. I will update once I head back over there.

 

Oh wait... I see what you mean. It’s not the knob being broken off, but the square shaft being disconnected from the valve that could be the issue. I wonder if he could have damaged it when turning it with pliers. It seemed to turn with the normal resistance when I did it last night.

 

I am also no A/C expert, but 75 on the low side with the system running in max A/C mode is way too high. Should be closer to 40-50 depending on outside temps. I wouldn't mess with measuring the highside, I would take it to an A/C shop for a diagnostic. Many offer the "summer tune-up specials" for a reasonable price. They can let you know if they find any issues. Sounds like you are overcharged though to start with.

 

This. A/C isn't difficult but without the proper tools and knowledge it's pretty easy to do some damage. Even the dealers here run a $30 AC inspection, last one I had done cost me $50 to add some refrigerant.

 

Do anyone know the part number/name of the valve on the firewall that’s connected to the temp control? I’m going to do a little more diagnostic (pinch off the coolant hose between the control and knob) and then put it in the shop if I can’t get anywhere. The shop is the last resort.

A friend told me these refill kits at AutoZone with the digital fill gauge can give false readings. This is the tool I used to measure the low side. Does anyone have experience with them?

 

I have a similar set of knobs as the ones @Tundra2 linked, since two of mine were broken when I bought the truck. They work very well... buy a set for your dad as a late Father's Day present.

When you adjust the middle Temperature knob two things should happen:
1) the coolant control valve that @Tundra2 showed in the pic opens/closes to regulate the flow of hot coolant to the heat exchanger in the cab.
2) the blend door in the HVAC system opens/closes to route air from the fan to/away from the heat exchanger.

To check #1, do as @Tundra2 suggested and look at the position of the valve under the hood, then go and change the position of the center control knob, then go observe the valve again. If the position of the valve changed, then that's working.

To check #2, lay on your back on the passenger side floor looking up at the HVAC system -- right above where the passenger's feet would be, toward the center. Move the heat control knob and see if the cable moves that actuates the blend door. If it moves, that's working.

Both of these tasks are more easily done with a helper. So if Dad is available, have him sit in the driver's seat and work the Temperature control.

 

Thank you for that explanation. I’ll be there tomorrow to go through all the suggested steps.

 

Bookmarking a few pages from the FSM. BTW, if anyone needs it (beware, it’s a resource hog on mobile): https://drive.google.com/file/d/0B9...aGM/view?resourcekey=0-IUgFBrEgIe9zfnbQv0LhaA

 

He stopped by for a quick minute today and I checked the water valve on the firewall. It functions normally. The right hose is hot and the left is just warm, if that matters.

Something he brought up- there is an ongoing issue with the main radiator fan where the clutch seems to be engaged and the fan runs just about all the time. Is this related to the AC issue? Could the constant running of the fan have damaged the AC compressor?

I also checked the sight glass on the cylindrical part where you can see the refrigerant bubbling. When the motor is held at 1500RPM, there is foaming present in the sight glass non-stop, when it’s supposed to appear and go away.

There’s a section in the FSM that uses the symptoms seen there to indicate what could be a problem. It says this indicates that the refrigerant is “low” which is weird considering I measured 75PSI on the low side. The section is attached below.

 

Radiator Fan will run all the time. How fast/slow is determined by Ambient Temp affecting the Silicone Oil inside and engaging/disengaging the coils. Should have nothing to do with your A/C and how it operates unless the fan isn’t pulling in air over the A/C Condenser at all (ie not working). If this was the case your Engine Radiator would overheat, as well.

As far as the Bubbles and your high PSI, I am unsure.

 

75 psi is too high. Low side too high and high side too low indicates compressor internal failure 90% of the time but you cannot see the high side in your case. Normal loss over a long period is expected. Evac and recharge most places is around 100-150 depending on location. If your technician pulls a vacuum on the system and it doesnt hold then you have a leak in which case they should not charge the system (further diag required). If it holds then they will charge it full with no air intrusion like you get with those garbage freon kits from local store. Worth it to take it in and theres a reason specialist are called well... specialists.

 

Agreed, I am an AC tech, Take it into a reliable shop and have them throw a set of gauges on it. They will be able to diagnose and will save you time and money.

 

What chain shops offer AC diagnostics and service? Like Midas, Mieneke, Jiffy Lube etc...

 

ice cold air does down here in FL. They charge 100 bucks to look at it no matter where you go to pay the tech for their time. IF you choose not to purchase the work, then you pay the diag. If you choose to do the job they wave the 100 bucks in most cases.

 

I have an appointment at Pep Boys next week. $63 diagnostic fee. I will update.