I had a high pressure issue with my a/c. This weekend I installed a new expansion valve, tested for restrictions, vacuumed, and charged with 2 1/3 12oz cans of R12, but the discharge air in the cabin isn’t cold. I believe I am getting warm air from the heater core. I stuck my head under the dash to check the operation of the blend door cable. It’s going all the way up again a vacuum actuated plunger that appears to me to be at the bottom of it’s travel.
Any ideas on what I need to look at or check? I know I have a vacuum issue or vacuum motor issue because I only get a little bit of air out of the center vents and most all comes out of the defrost, but figured I would get cold air first then worry about where it’s going.
You should have a valve in the heater hose under the hood up against the firewall(usually gold colored) to shutoff the flow of hot water to the core. If there you need to check the vacuum going to it from the blend door valve. Usually with only air coming out of the defrost the vacuum system is not working. A long time Ford mechanic said the system was designed if the vacuum failed the default was to defrost to keep windows clear.
I do have the valve. I had it wire-tied closed before, like if vacuum was pulling. I cut the zip tie and it didn’t make a difference. I did notice both heater hoses were hot; not sure if the valve was functioning correctly if the hose behind it would have any heat in it or not?
I’m thinking I am at least getting some vacuum because I get a little air out the center registers and when I use the heat I can switch it to floor mode. I had a work van years ago that only had defrost, the company got it fixed, but I bet it didn’t have vacuum. My winter car is a '98 Jeep Cherokee when I got it air only came out the defrost, I found a disconnected vacuum line and it returned full function to the controls. I think they are all made to where if they lose vacuum they default to defrost, might even be gov’t mandate.
I thought my 1970 manual said 1 3/4 pounds, but I also did a quick internet search and saw a couple places people said 2 3/4 pounds. I’ll have to re-check the manual tonight, thanks for bringing this up.
Look what I just found on WCCC, tells factory capacity, but as you mentioned people say 2 3/4# Yesterday after we put 1 3/4# I thought R12 was cold enough to make the lines glaze up with ice, but I didn’t see any. Soooo, maybe factory capacity is 1 3/4#, but they will hold more and are colder with more?
Last night I started the car, the engine hadn’t been ran for the day so no heat in it. I turned the A/C on and it was colder than the night before because the engine wasn’t putting off any heat yet. I was thinking of pinching off one of the heater core feed hoses, but didn’t want to pinch the wrong one and risk damaging the core. I am going to order a new water control valve that goes inline to one of the heater lines. I thought about looping one of the hoses back, but didn’t want to mess with spilling coolant, topping off and then doing it again in a few days when the new water control valve comes in.
I started looking at the vacuum lines under the dash, but there is a bunch of them and I think I might be best to start off by pulling the heat/ac control and starting there. Is that where the one from the firewall goes to? I found the vacuum motor responsible for switching air to the dash vents, I manually activated it and air blew out of the dash vents.
I ordered a replacement water control valve. Someone put it on the hose that comes out of the core and goes to the water pump. I read somewhere online that it goes in the heater hose that comes off of the intake manifold. To me it makes more sense to go in the line off the intake manifold. Can someone tell me which is correct?
Well I’m back at it. I had a couple problems with the A/C system that I fixed in the past week. I charged the system with the proper 1.75 # of R12. I believe the system is working properly because the inlet and outlet of the evaporator core are getting frost on them.
I think I am not getting good airflow, from the blower motor, across the evaporator core. The reason I say this is because the de-icing switch is shutting off the compressor but it’s shutting off when the temperature out of the center vent is 48 degrees. From what I’ve heard about R12 it would freeze you out and I kind of remember this as a kid in my grandparent’s 1978 Thunderbird.
Is there a way I can get to the evaporator core to vacuum or blow it off without pulling the hvac box? I thought I could remove the blower motor and get inside the box but from the diagrams I saw I think the heater core will be in the way. My other thought was to remove the screws that hold the cowl cover on but not sure if that would get me to the evaporator core or not.
Any guidance, recommendations, or opinions are appreciated!
A little late to this A/C thread, and for what it’s worth ( to future readers / searches that might want ) to see what the hot water shut-off valve ( stamped C9AA-18495-D / p/n’s C9AZ or D1AZ-18495-B ) looks like:
Anyone know a way I can access the evaporator core area of the hvac box?
I was thinking of getting a borescope and running it over to the evaporator core by removing the fan. I’m not sure if I would even be able to get there with a borescope.
Unfortunately I don’t know an easy way to do this. Your complaint is about poor airflow - everything is vacuum actuated and the airflow depends on the actuators working properly. If your headlight motors do not work properly they can leak a lot of vacuum. I would disconnect them at the intake and plug the hole and try that. The other typical issue is the AC vacuum can leaks. Reproductions are available - but they also are known to fail. Be sure to test any reproduction vacuum tank immediately.
