[Bobby78]

OK I give up! Can't understand what I'm doing wrong. Should be a simple thing. I would think.
Put a new Factory Air switch part # 35720 in there a few weeks ago. Worked for a little while and then starting freezing again in cooler weather at night on the highway. OK tried to adjust it again and lost one of the screws. Went to buy another switch and could only get an AC Delco. The delco had one adjusting screw and regardless of which direction or how far I turned it, the compressor would never shut off.
Ordered a new factory air switch and put it on today. AC running, pulled the power off the fan to make evap freeze. This switch has 2 screws. One says "cut in" and the other "cut out". Evap ices up. Low Side drops down to 10 psi and compressor won't cut out. Tried adjusting screws nothing happens. Pull the plug off the switch and the compressor stops.
So, picking up heat in the engine compartment? Don't think so. I have planty of cork tape over the bulb and about 4 inches of the wire. Covered that in heavy rubber electrical tape. Tried adjusting again. I can get it to cycle on/off but it doesn't hold the settings. If I get to go off at 30 psi the next time I try it just keeps running. If I get it to kick in at at 50 psi the next time I try it it runs up to 75 psi and still doesn't come on. Kept playing with the screws until boingggg!!!! One goes flying. OK took the other one from the old switch and started over. But can't get a consistent setting.
So what am I doing wrong?
Can someone recommend a better switch that this $15 POS? The delco seemed better built but I couldn't get to work right either. Is the problem that they're set for R-134a and not R-12 anymore? Either way I would think it's sensing temp. So freezing is still freezing.

 

[acauth1]

Bobby, I still think you are low on charge. Feel the evaporator inlet (the small line) and the evaporator outlet (goes to accumulator), they should feel about the same temp. If the outlet is warmer, you're undercharged. As far as the thermostatic switch is concerned, the ones with the small adjustment screws are for very fine tuning only, you will not get more than a turn or so on each at best. Thermostatic switches don't care what type of refrigerant you use, temperature is temperature and ice still forms on the evaporator around 32*. Like I said before, you need the type of switch used on the old knee-knocker underdash units if you want adjustment:

http://www.oreillyauto.com/site/c/detail/MRY0/35845.oap?ck=Search_35845_-1_1323&keyword=35845

 

[Bobby78]

Well it's not that "I want" adjustment. It's just that I don't want it freezing up after 10 minutes on the highway.
So why don't the replacement switches cycle the compressor before the evap freezes?

 

[acauth1]

The switch is intended to "make" or "break" the power circuit to the clutch depending on evaporator temperature as you well know. It's possible that the two green wires to the switch are intermittently shorting together thus bypassing the switch altogether. If multiple switches have not solved the issue then it's time to look elsewhere for the problem.

 

[Bobby78]

I'll check the wiring but I don't think that's it either. If I turn the screws enough, I can get it to cylce. The problem is when I adjust the "cut out" switch the "cut in" loses it's setting. When I readjust the "cut in", I lose the "cut out".

 

[Bobby78]

The problem I've had with the switches is they all cycle off at 0 psi. By then the evap is a block of ice. First switch was the factory air switch with the 2 adjusting screws. They are small brass screws threaded into a plastic housing. After turning them a few times the plastic housing strips and the screw goes flying. Bought a delco. Same as OEM only 1 screw. This one cycles off at 0 psi also. Tried adjusting that, stripped that screw too. Bought another factory air switch. Almost had it where I thought it was working and stripped that one too. So yeah the switches are not made to take adjustment. But 0 psi cut out is way too low, isn't it?
Anyway, I can't keep buying switches everyday.

 

[Bobby78]

OK ordered that one you linked above from o'reilly's. Should have it Wednesday.
BTW, maybe you could help me with another thing? There are 2 vacuum "switches" that mount on the back of the selector switch housing. One of them is on the left side and about 2 vacuum hose connections. The other is on the right and is a round switch that has a bunch of vacuum lines connected to it. I've seen what look to be the same replacements on ebay but when I enter make/model they say these don't fit. Would you know the correct part #'s?
Mine are getting a bit worn I think as there is a delayed reaction in switching vent positions. If I squeeze the round switch it switches immediately.

 

[acauth1]

Bobby,

ecparts.net

Nine port switch EN 1301
Two port switch EN 1302

 

[Bobby78]

OK thanks!

 

[Bobby78]

Ok new problem. Added some R12. Now LS 55 psi and HS 280-300 +
Outside temp 96* very humid. vent temps 57.4

 

[Bobby78]

Recovered some R12. Pressure LS 35 & HS 215
Now accumulator and evap pipes are warm. Vent temps 63. But heater core is getting hot water. So that could explain the higher vent temps. Going to order vacuum switches tomorrow. Maybe I'll just run a vacuum line from heatercontrol valve to manifold and close that offfor now.

 

[Bobby78]

Took it for a ride. Vent temps came down to 50-52 on side streets. Jumped on the highway and upon accelleration temps went up to 68. Settled in at a cruising speed of 55 and temps dropped to 49-51. Off the highway, around town again, 48-50.
But still coolant flowing through the heater core. So that could explain some of that.

 

[skybu]

Took it for a ride. Vent temps came down to 50-52 on side streets. Jumped on the highway and upon accelleration temps went up to 68. Settled in at a cruising speed of 55 and temps dropped to 49-51. Off the highway, around town again, 48-50.
But still coolant flowing through the heater core. So that could explain some of that.

What was your outside temp when you took these readings ?
I am having a similar problem but it is super hot down here in texas right now.
I just installed a new four seasons compressor because the old one leaked out ALL of my r12 over the winter. It is not getting as cold as I would like for it to.
about 55 degree sitting still but it raises to about 65 going down the highway 75mph.
100 degree outside temp.
when I was chargeing it was high humidity and 98 degrees.
ls30,hs 210
Do I need more Freon ?

 

[Bobby78]

It was about 96* here yesterday and very high humidity. Today after last nights heavy storms, vent temps in the mid 40's, outside temp 88* and low humidity.

 

[acauth1]

Have you solved the coolant flow through heater core issue yet?

 

[Bobby78]

No waiting for the parts for the switch. Should be here thursday/friday. If I get a chance, I'll get a piece of vac hose and just run from the manifold to the valve to see if it helps.