A/C and heat problem

[mjr45]

I've searched the threads for an answer and come empty. All the vacuum lines to the heat control have been checked and/or replaced. The A/C has been recharged and shows 70 lbs. of pressure. All the wire controlled valves and flappers are working. What I get is no cold air and no heat. Sometimes I get cool air thru the defrost vents and from the bottom vents when set to heat, I can also get cool air from the center vents at times unless the control is first put to defrost and the back to other settings. I'm lost once again!

[71Nissan240Z]

Thats way too much pressure. The compressor cannot work well when u overcharge the system. You need to refer to the manual on the pump. Most cars take two to three small cans of stuff. Everytime i service an ac unit the low side is around 30-40 psi and the high is 150-200 psi with a temp around 80degrees ambient. Did u evac the system before hand? Its important. But with a proper fill of r-12 the pressure readings should be a little bit lower than r134a. You should be sitting around 35-45 degrees blowing out the vents with a proper charge. Clean condensor and very good fan. Doing ac work is tricky. I just replaced a blown compressor last night from a guy thinking his system was empty and overfilled. Seems as his original problem was just a bad expansion valve. I really dont know why those places sell those cans. You really cant just fill it up and go.

[hr369]

That 70 psi may be a typo or static

Pressure. If not a typo stop using it

Immediately.

[mjr45]

Yup I know the pressure is to high, according to the FSM it shouldn't be over 40. Tomorrow, I'll evacuate the system and try again, I alos didn't hear the compressor engaging, but that may be a function of the pressure.

[mjr45]

Any idea's on the heating problems. The heater worked fine 2 weeks ago when checked, now it just blows cool air but only after putting the control to defrost then back to heat. All the vacuum lines are good and no loose connections. I can do without the A/C, but not the heat. Like I said, I'm stuck!

[71Nissan240Z]

The hot cold control blend switches need to be checked regarding the heater. Your ac...you have a low pressure switch. It might be bad. Also check ur expansion valve. It is whats used to meter the freon into ur condensor. Sometimes its an orifice tube. Your accumulator or dryer might need to be changed too. I would just replace all of these. Also turn the compressor pump manually with ur hand to see compression.

[mjr45]

I'm totally f*****g baffled, if I start the car with the control in the A/C position I get air from the center and floor vents, when I move the control to REC I get air from the floor vents, when I move the control back to A/C no air from the center vents only from the floor, if I shut her down and restart I get air back to the center vents. I tried to flush the heater core, it would flush thru the return line but not the intake and the two lines on the interior to the core are stone cold. The lines in the engine bay are warm, but probably just from engine heat. Its got a new water pump and never runs hot so WTF is going on????

Edited July 4, 2013 by mjr45

[Zed Head]

Have you checked the magnet valves (solenoids) for proper operation? That's where the vacuum is distributed to the hoses and actuators. Maybe you have one that's sticking and not opening to atmosphere to release the vacuum.

[mjr45]

Zed, I haven't checked them, I'm not real sure how to. Just got done reading the FSM A/C section and I'm as confused as ever. The trouble shooting guides don't seem to answer my questions about to check. I may have a spare set of magnet valves so I'll have to dig around in my spares boxes.

[zKars]

Vacuum runs it all. Check for lines and hoses off and cracked ends.

[mjr45]

z, I already have, the lines have all been checked and about 75% replaced with new line.

[mjr45]

Just to kill this thread, I found a tiny tiny crack in the vacuum line going thru the firewall to the control valve, The line was cracked right where it met the firewall. Now all is well. thanks for all the help.