Car stalls when A/C is switched on

Just had the A/C in my 70 GS455 done and when I turn it on at normal idle the engine wants to stall. I've been reading several threads trying to figure this out and some said that 1970 and earlier used a "dashpot". Could someone please let me know what it is, how it works, and hopefully suggest a source for one? I was going to put an idle speed solenoid on but apparently that's wrong for the year. Thanks.

 

The 70 dashpot did not raise idle with the AC on. It simply slowed the closing of the throttle under all conditions. Later cars had the idle speed solonoid which did actually increase the idle with the AC on.

 

An over charged a/c can cause this. Or a plugged expansion valve. It slugs the compressor causing it to stall the motor.

 

David, Could too much oil in the system cause this? When the A/C mech. first got it up and running it had back pressure in the system. They found there was too much oil in the system. I'm wondering if they drained enough of it out.... Robert

 

Thanks Nicholas. I think I already have one towards the back on the passenger side of the carb. Robert

 

OH ya!!! What happens is it gets into the expansion or (POA) valve and causes the high side to spike. That will cause slugging in the compressor. Or it's from the previous over filled oil and it has clogged the valves. Contrary to what some may say you can remove the valves and clean them out. I did mine on my 69 and charged it with Freeze12 and I get a nice 48 degree blow from the vents.

 

Fast idle AC solenoid appeared in 71 and replaced the 70 dash pot. The green power wire for the ac compress has a splice that send a green wire to the solenoid. When compressor is turned on, the solenoid is energized.

The POA is not the expansion valve. Expansion valve is located below the POA valve. The POA is (Pilot Operated Actuator) allows the system to go into bypass mode when/if the expansion valve freezes preventing the compressor from grenading.

 

George was that solenoid just for 4 speed cars in 71? My 71 Auto Stage-1 did not have that solenoid and the service manual just shows th dashpot for an auto.

 

Changeover happened in 71, I believe Steve Craig stated mid-71 was first design introduction. Late 71 and thru 77 used the same solenoid.

 

Sorry I meant to put an "or" in there. ou:

My bad.. I fixed it.

But if there is any build up of oil in those valves it will cause the high side pressure to go through the roof and stall the car even if the solenoid is working. :TU:

 

Thanks everyone. Looks like it's going back to the shop.

 

David, Is there a difference between regular R12 and freeze12? Mine is getting cold but nowhere near 48 degrees. I understand it's probably due to the blockage as well. They said they drained the system but didn't mention cleaning the POA valves. They did put a new expansion valve in. Robert

 

Yes there is a difference. About 30 dollars a pound. p p

My brother is the mechanic in the family. He explained it to me but he might as well been speaking greek. uzzled:

But he says he finds much cooler temps coming from Freeze12 units with less pressures. I had R12 in there and I got 55 degree temps with close to a 200psi high and a 40psi low. Now with the same system with the Freeze12 I get the 48 degrees with 180psi high and 28psi low. This was with 81 degrees in the shop. Your pressures will rise with the ambient temp. :TU:

http://www.freeze12.com/

Look I had the frickin bottle up the first time. ou:

Filled the system with gas.

LOL!!! :laugh: :laugh:

 

check this out, R-500. 20% more capacity than R-12 with a very close temp/press relationship and was designed for mineral oil. It's also cheaper than R-12.

 

I live in Florida. I would think the lower pressures would be ideal here due to the high outdoor temps in the summer. I would think it also helps to prolong the system. Can you buy it retail or is it only available wholesale? I would have done the same thing with the bottle! Thanks for this info. Robert

 

Is there a benefit to it over the freeze-12 product?