A/C intermittent at times??

[Cadillacmob]

On my 85 Marquis when the cars ideling, or just cruiseing AC blows ice cold. However when i step on it a little the blower motor will stop blowing on HI and blow low and hot air will come out. when i let my foot off and maintain a steady speed the ac blows perfectly .

I never had this car in the summer untill this one so i have no idea how the ac worked prior to me owning the car.

i deleated the smog pump and got a smaller belt so i thought maybe the belt was slipping but it seems like its pretty tight.

Any ideas ?

[mercurygm88]

Sounds like a vacuum leak whereas the blower speed isn't changing but the vents are trying to switch to defrost due to lack if vacuum. If you lose vacuum the vents will default to hot defrost. I had this exact problem on my 88 and it was the little hvac check valve near the firewall. Follow the vacuum line from the soup can and you will find the check valve. I got my replacement from my local ford dealer for $10. I don't have the part # but have found similar check valves at my local oreillys and napa I'll see if I can find you a pic of one.

[mercurygm88]

Unfortunately I am not having any luck locating one, hopefully someone else will come along and be able to help.

[gadget73]

Automatic climate control, or manual? if its auto, it definitely sounds like a leak. Check the soup can, the thermal blower lockout (its the thing in the heater hose with 2 wires and 2 vacuum lines) and the check valve at the firewall. If any of those things are leaky or bad, as soon as the system loses vacuum, such as when you give it some throttle, it defaults to hot defrost.